/* * Generic process-grouping system. * * Based originally on the cpuset system, extracted by Paul Menage * Copyright (C) 2006 Google, Inc * * Notifications support * Copyright (C) 2009 Nokia Corporation * Author: Kirill A. Shutemov * * Copyright notices from the original cpuset code: * -------------------------------------------------- * Copyright (C) 2003 BULL SA. * Copyright (C) 2004-2006 Silicon Graphics, Inc. * * Portions derived from Patrick Mochel's sysfs code. * sysfs is Copyright (c) 2001-3 Patrick Mochel * * 2003-10-10 Written by Simon Derr. * 2003-10-22 Updates by Stephen Hemminger. * 2004 May-July Rework by Paul Jackson. * --------------------------------------------------- * * This file is subject to the terms and conditions of the GNU General Public * License. See the file COPYING in the main directory of the Linux * distribution for more details. */ #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include /* TODO: replace with more sophisticated array */ #include #include #include /* * pidlists linger the following amount before being destroyed. The goal * is avoiding frequent destruction in the middle of consecutive read calls * Expiring in the middle is a performance problem not a correctness one. * 1 sec should be enough. */ #define CGROUP_PIDLIST_DESTROY_DELAY HZ #define CGROUP_FILE_NAME_MAX (MAX_CGROUP_TYPE_NAMELEN + \ MAX_CFTYPE_NAME + 2) /* * cgroup_tree_mutex nests above cgroup_mutex and protects cftypes, file * creation/removal and hierarchy changing operations including cgroup * creation, removal, css association and controller rebinding. This outer * lock is needed mainly to resolve the circular dependency between kernfs * active ref and cgroup_mutex. cgroup_tree_mutex nests above both. */ static DEFINE_MUTEX(cgroup_tree_mutex); /* * cgroup_mutex is the master lock. Any modification to cgroup or its * hierarchy must be performed while holding it. * * css_set_rwsem protects task->cgroups pointer, the list of css_set * objects, and the chain of tasks off each css_set. * * These locks are exported if CONFIG_PROVE_RCU so that accessors in * cgroup.h can use them for lockdep annotations. */ #ifdef CONFIG_PROVE_RCU DEFINE_MUTEX(cgroup_mutex); DECLARE_RWSEM(css_set_rwsem); EXPORT_SYMBOL_GPL(cgroup_mutex); EXPORT_SYMBOL_GPL(css_set_rwsem); #else static DEFINE_MUTEX(cgroup_mutex); static DECLARE_RWSEM(css_set_rwsem); #endif /* * Protects cgroup_subsys->release_agent_path. Modifying it also requires * cgroup_mutex. Reading requires either cgroup_mutex or this spinlock. */ static DEFINE_SPINLOCK(release_agent_path_lock); #define cgroup_assert_mutexes_or_rcu_locked() \ rcu_lockdep_assert(rcu_read_lock_held() || \ lockdep_is_held(&cgroup_tree_mutex) || \ lockdep_is_held(&cgroup_mutex), \ "cgroup_[tree_]mutex or RCU read lock required"); /* * cgroup destruction makes heavy use of work items and there can be a lot * of concurrent destructions. Use a separate workqueue so that cgroup * destruction work items don't end up filling up max_active of system_wq * which may lead to deadlock. */ static struct workqueue_struct *cgroup_destroy_wq; /* * pidlist destructions need to be flushed on cgroup destruction. Use a * separate workqueue as flush domain. */ static struct workqueue_struct *cgroup_pidlist_destroy_wq; /* generate an array of cgroup subsystem pointers */ #define SUBSYS(_x) [_x ## _cgrp_id] = &_x ## _cgrp_subsys, static struct cgroup_subsys *cgroup_subsys[] = { #include }; #undef SUBSYS /* array of cgroup subsystem names */ #define SUBSYS(_x) [_x ## _cgrp_id] = #_x, static const char *cgroup_subsys_name[] = { #include }; #undef SUBSYS /* * The default hierarchy, reserved for the subsystems that are otherwise * unattached - it never has more than a single cgroup, and all tasks are * part of that cgroup. */ struct cgroup_root cgrp_dfl_root; /* * The default hierarchy always exists but is hidden until mounted for the * first time. This is for backward compatibility. */ static bool cgrp_dfl_root_visible; /* The list of hierarchy roots */ static LIST_HEAD(cgroup_roots); static int cgroup_root_count; /* hierarchy ID allocation and mapping, protected by cgroup_mutex */ static DEFINE_IDR(cgroup_hierarchy_idr); /* * Assign a monotonically increasing serial number to cgroups. It * guarantees cgroups with bigger numbers are newer than those with smaller * numbers. Also, as cgroups are always appended to the parent's * ->children list, it guarantees that sibling cgroups are always sorted in * the ascending serial number order on the list. Protected by * cgroup_mutex. */ static u64 cgroup_serial_nr_next = 1; /* This flag indicates whether tasks in the fork and exit paths should * check for fork/exit handlers to call. This avoids us having to do * extra work in the fork/exit path if none of the subsystems need to * be called. */ static int need_forkexit_callback __read_mostly; static struct cftype cgroup_base_files[]; static void cgroup_put(struct cgroup *cgrp); static int rebind_subsystems(struct cgroup_root *dst_root, unsigned long ss_mask); static void cgroup_destroy_css_killed(struct cgroup *cgrp); static int cgroup_destroy_locked(struct cgroup *cgrp); static int cgroup_addrm_files(struct cgroup *cgrp, struct cftype cfts[], bool is_add); static void cgroup_pidlist_destroy_all(struct cgroup *cgrp); /** * cgroup_css - obtain a cgroup's css for the specified subsystem * @cgrp: the cgroup of interest * @ss: the subsystem of interest (%NULL returns the dummy_css) * * Return @cgrp's css (cgroup_subsys_state) associated with @ss. This * function must be called either under cgroup_mutex or rcu_read_lock() and * the caller is responsible for pinning the returned css if it wants to * keep accessing it outside the said locks. This function may return * %NULL if @cgrp doesn't have @subsys_id enabled. */ static struct cgroup_subsys_state *cgroup_css(struct cgroup *cgrp, struct cgroup_subsys *ss) { if (ss) return rcu_dereference_check(cgrp->subsys[ss->id], lockdep_is_held(&cgroup_tree_mutex) || lockdep_is_held(&cgroup_mutex)); else return &cgrp->dummy_css; } /* convenient tests for these bits */ static inline bool cgroup_is_dead(const struct cgroup *cgrp) { return test_bit(CGRP_DEAD, &cgrp->flags); } struct cgroup_subsys_state *seq_css(struct seq_file *seq) { struct kernfs_open_file *of = seq->private; struct cgroup *cgrp = of->kn->parent->priv; struct cftype *cft = seq_cft(seq); /* * This is open and unprotected implementation of cgroup_css(). * seq_css() is only called from a kernfs file operation which has * an active reference on the file. Because all the subsystem * files are drained before a css is disassociated with a cgroup, * the matching css from the cgroup's subsys table is guaranteed to * be and stay valid until the enclosing operation is complete. */ if (cft->ss) return rcu_dereference_raw(cgrp->subsys[cft->ss->id]); else return &cgrp->dummy_css; } EXPORT_SYMBOL_GPL(seq_css); /** * cgroup_is_descendant - test ancestry * @cgrp: the cgroup to be tested * @ancestor: possible ancestor of @cgrp * * Test whether @cgrp is a descendant of @ancestor. It also returns %true * if @cgrp == @ancestor. This function is safe to call as long as @cgrp * and @ancestor are accessible. */ bool cgroup_is_descendant(struct cgroup *cgrp, struct cgroup *ancestor) { while (cgrp) { if (cgrp == ancestor) return true; cgrp = cgrp->parent; } return false; } static int cgroup_is_releasable(const struct cgroup *cgrp) { const int bits = (1 << CGRP_RELEASABLE) | (1 << CGRP_NOTIFY_ON_RELEASE); return (cgrp->flags & bits) == bits; } static int notify_on_release(const struct cgroup *cgrp) { return test_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags); } /** * for_each_css - iterate all css's of a cgroup * @css: the iteration cursor * @ssid: the index of the subsystem, CGROUP_SUBSYS_COUNT after reaching the end * @cgrp: the target cgroup to iterate css's of * * Should be called under cgroup_mutex. */ #define for_each_css(css, ssid, cgrp) \ for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT; (ssid)++) \ if (!((css) = rcu_dereference_check( \ (cgrp)->subsys[(ssid)], \ lockdep_is_held(&cgroup_tree_mutex) || \ lockdep_is_held(&cgroup_mutex)))) { } \ else /** * for_each_subsys - iterate all enabled cgroup subsystems * @ss: the iteration cursor * @ssid: the index of @ss, CGROUP_SUBSYS_COUNT after reaching the end */ #define for_each_subsys(ss, ssid) \ for ((ssid) = 0; (ssid) < CGROUP_SUBSYS_COUNT && \ (((ss) = cgroup_subsys[ssid]) || true); (ssid)++) /* iterate across the hierarchies */ #define for_each_root(root) \ list_for_each_entry((root), &cgroup_roots, root_list) /** * cgroup_lock_live_group - take cgroup_mutex and check that cgrp is alive. * @cgrp: the cgroup to be checked for liveness * * On success, returns true; the mutex should be later unlocked. On * failure returns false with no lock held. */ static bool cgroup_lock_live_group(struct cgroup *cgrp) { mutex_lock(&cgroup_mutex); if (cgroup_is_dead(cgrp)) { mutex_unlock(&cgroup_mutex); return false; } return true; } /* the list of cgroups eligible for automatic release. Protected by * release_list_lock */ static LIST_HEAD(release_list); static DEFINE_RAW_SPINLOCK(release_list_lock); static void cgroup_release_agent(struct work_struct *work); static DECLARE_WORK(release_agent_work, cgroup_release_agent); static void check_for_release(struct cgroup *cgrp); /* * A cgroup can be associated with multiple css_sets as different tasks may * belong to different cgroups on different hierarchies. In the other * direction, a css_set is naturally associated with multiple cgroups. * This M:N relationship is represented by the following link structure * which exists for each association and allows traversing the associations * from both sides. */ struct cgrp_cset_link { /* the cgroup and css_set this link associates */ struct cgroup *cgrp; struct css_set *cset; /* list of cgrp_cset_links anchored at cgrp->cset_links */ struct list_head cset_link; /* list of cgrp_cset_links anchored at css_set->cgrp_links */ struct list_head cgrp_link; }; /* * The default css_set - used by init and its children prior to any * hierarchies being mounted. It contains a pointer to the root state * for each subsystem. Also used to anchor the list of css_sets. Not * reference-counted, to improve performance when child cgroups * haven't been created. */ static struct css_set init_css_set = { .refcount = ATOMIC_INIT(1), .cgrp_links = LIST_HEAD_INIT(init_css_set.cgrp_links), .tasks = LIST_HEAD_INIT(init_css_set.tasks), .mg_tasks = LIST_HEAD_INIT(init_css_set.mg_tasks), .mg_preload_node = LIST_HEAD_INIT(init_css_set.mg_preload_node), .mg_node = LIST_HEAD_INIT(init_css_set.mg_node), }; static int css_set_count = 1; /* 1 for init_css_set */ /* * hash table for cgroup groups. This improves the performance to find * an existing css_set. This hash doesn't (currently) take into * account cgroups in empty hierarchies. */ #define CSS_SET_HASH_BITS 7 static DEFINE_HASHTABLE(css_set_table, CSS_SET_HASH_BITS); static unsigned long css_set_hash(struct cgroup_subsys_state *css[]) { unsigned long key = 0UL; struct cgroup_subsys *ss; int i; for_each_subsys(ss, i) key += (unsigned long)css[i]; key = (key >> 16) ^ key; return key; } static void put_css_set_locked(struct css_set *cset, bool taskexit) { struct cgrp_cset_link *link, *tmp_link; lockdep_assert_held(&css_set_rwsem); if (!atomic_dec_and_test(&cset->refcount)) return; /* This css_set is dead. unlink it and release cgroup refcounts */ hash_del(&cset->hlist); css_set_count--; list_for_each_entry_safe(link, tmp_link, &cset->cgrp_links, cgrp_link) { struct cgroup *cgrp = link->cgrp; list_del(&link->cset_link); list_del(&link->cgrp_link); /* @cgrp can't go away while we're holding css_set_rwsem */ if (list_empty(&cgrp->cset_links) && notify_on_release(cgrp)) { if (taskexit) set_bit(CGRP_RELEASABLE, &cgrp->flags); check_for_release(cgrp); } kfree(link); } kfree_rcu(cset, rcu_head); } static void put_css_set(struct css_set *cset, bool taskexit) { /* * Ensure that the refcount doesn't hit zero while any readers * can see it. Similar to atomic_dec_and_lock(), but for an * rwlock */ if (atomic_add_unless(&cset->refcount, -1, 1)) return; down_write(&css_set_rwsem); put_css_set_locked(cset, taskexit); up_write(&css_set_rwsem); } /* * refcounted get/put for css_set objects */ static inline void get_css_set(struct css_set *cset) { atomic_inc(&cset->refcount); } /** * compare_css_sets - helper function for find_existing_css_set(). * @cset: candidate css_set being tested * @old_cset: existing css_set for a task * @new_cgrp: cgroup that's being entered by the task * @template: desired set of css pointers in css_set (pre-calculated) * * Returns true if "cset" matches "old_cset" except for the hierarchy * which "new_cgrp" belongs to, for which it should match "new_cgrp". */ static bool compare_css_sets(struct css_set *cset, struct css_set *old_cset, struct cgroup *new_cgrp, struct cgroup_subsys_state *template[]) { struct list_head *l1, *l2; if (memcmp(template, cset->subsys, sizeof(cset->subsys))) { /* Not all subsystems matched */ return false; } /* * Compare cgroup pointers in order to distinguish between * different cgroups in heirarchies with no subsystems. We * could get by with just this check alone (and skip the * memcmp above) but on most setups the memcmp check will * avoid the need for this more expensive check on almost all * candidates. */ l1 = &cset->cgrp_links; l2 = &old_cset->cgrp_links; while (1) { struct cgrp_cset_link *link1, *link2; struct cgroup *cgrp1, *cgrp2; l1 = l1->next; l2 = l2->next; /* See if we reached the end - both lists are equal length. */ if (l1 == &cset->cgrp_links) { BUG_ON(l2 != &old_cset->cgrp_links); break; } else { BUG_ON(l2 == &old_cset->cgrp_links); } /* Locate the cgroups associated with these links. */ link1 = list_entry(l1, struct cgrp_cset_link, cgrp_link); link2 = list_entry(l2, struct cgrp_cset_link, cgrp_link); cgrp1 = link1->cgrp; cgrp2 = link2->cgrp; /* Hierarchies should be linked in the same order. */ BUG_ON(cgrp1->root != cgrp2->root); /* * If this hierarchy is the hierarchy of the cgroup * that's changing, then we need to check that this * css_set points to the new cgroup; if it's any other * hierarchy, then this css_set should point to the * same cgroup as the old css_set. */ if (cgrp1->root == new_cgrp->root) { if (cgrp1 != new_cgrp) return false; } else { if (cgrp1 != cgrp2) return false; } } return true; } /** * find_existing_css_set - init css array and find the matching css_set * @old_cset: the css_set that we're using before the cgroup transition * @cgrp: the cgroup that we're moving into * @template: out param for the new set of csses, should be clear on entry */ static struct css_set *find_existing_css_set(struct css_set *old_cset, struct cgroup *cgrp, struct cgroup_subsys_state *template[]) { struct cgroup_root *root = cgrp->root; struct cgroup_subsys *ss; struct css_set *cset; unsigned long key; int i; /* * Build the set of subsystem state objects that we want to see in the * new css_set. while subsystems can change globally, the entries here * won't change, so no need for locking. */ for_each_subsys(ss, i) { if (root->cgrp.subsys_mask & (1UL << i)) { /* Subsystem is in this hierarchy. So we want * the subsystem state from the new * cgroup */ template[i] = cgroup_css(cgrp, ss); } else { /* Subsystem is not in this hierarchy, so we * don't want to change the subsystem state */ template[i] = old_cset->subsys[i]; } } key = css_set_hash(template); hash_for_each_possible(css_set_table, cset, hlist, key) { if (!compare_css_sets(cset, old_cset, cgrp, template)) continue; /* This css_set matches what we need */ return cset; } /* No existing cgroup group matched */ return NULL; } static void free_cgrp_cset_links(struct list_head *links_to_free) { struct cgrp_cset_link *link, *tmp_link; list_for_each_entry_safe(link, tmp_link, links_to_free, cset_link) { list_del(&link->cset_link); kfree(link); } } /** * allocate_cgrp_cset_links - allocate cgrp_cset_links * @count: the number of links to allocate * @tmp_links: list_head the allocated links are put on * * Allocate @count cgrp_cset_link structures and chain them on @tmp_links * through ->cset_link. Returns 0 on success or -errno. */ static int allocate_cgrp_cset_links(int count, struct list_head *tmp_links) { struct cgrp_cset_link *link; int i; INIT_LIST_HEAD(tmp_links); for (i = 0; i < count; i++) { link = kzalloc(sizeof(*link), GFP_KERNEL); if (!link) { free_cgrp_cset_links(tmp_links); return -ENOMEM; } list_add(&link->cset_link, tmp_links); } return 0; } /** * link_css_set - a helper function to link a css_set to a cgroup * @tmp_links: cgrp_cset_link objects allocated by allocate_cgrp_cset_links() * @cset: the css_set to be linked * @cgrp: the destination cgroup */ static void link_css_set(struct list_head *tmp_links, struct css_set *cset, struct cgroup *cgrp) { struct cgrp_cset_link *link; BUG_ON(list_empty(tmp_links)); link = list_first_entry(tmp_links, struct cgrp_cset_link, cset_link); link->cset = cset; link->cgrp = cgrp; list_move(&link->cset_link, &cgrp->cset_links); /* * Always add links to the tail of the list so that the list * is sorted by order of hierarchy creation */ list_add_tail(&link->cgrp_link, &cset->cgrp_links); } /** * find_css_set - return a new css_set with one cgroup updated * @old_cset: the baseline css_set * @cgrp: the cgroup to be updated * * Return a new css_set that's equivalent to @old_cset, but with @cgrp * substituted into the appropriate hierarchy. */ static struct css_set *find_css_set(struct css_set *old_cset, struct cgroup *cgrp) { struct cgroup_subsys_state *template[CGROUP_SUBSYS_COUNT] = { }; struct css_set *cset; struct list_head tmp_links; struct cgrp_cset_link *link; unsigned long key; lockdep_assert_held(&cgroup_mutex); /* First see if we already have a cgroup group that matches * the desired set */ down_read(&css_set_rwsem); cset = find_existing_css_set(old_cset, cgrp, template); if (cset) get_css_set(cset); up_read(&css_set_rwsem); if (cset) return cset; cset = kzalloc(sizeof(*cset), GFP_KERNEL); if (!cset) return NULL; /* Allocate all the cgrp_cset_link objects that we'll need */ if (allocate_cgrp_cset_links(cgroup_root_count, &tmp_links) < 0) { kfree(cset); return NULL; } atomic_set(&cset->refcount, 1); INIT_LIST_HEAD(&cset->cgrp_links); INIT_LIST_HEAD(&cset->tasks); INIT_LIST_HEAD(&cset->mg_tasks); INIT_LIST_HEAD(&cset->mg_preload_node); INIT_LIST_HEAD(&cset->mg_node); INIT_HLIST_NODE(&cset->hlist); /* Copy the set of subsystem state objects generated in * find_existing_css_set() */ memcpy(cset->subsys, template, sizeof(cset->subsys)); down_write(&css_set_rwsem); /* Add reference counts and links from the new css_set. */ list_for_each_entry(link, &old_cset->cgrp_links, cgrp_link) { struct cgroup *c = link->cgrp; if (c->root == cgrp->root) c = cgrp; link_css_set(&tmp_links, cset, c); } BUG_ON(!list_empty(&tmp_links)); css_set_count++; /* Add this cgroup group to the hash table */ key = css_set_hash(cset->subsys); hash_add(css_set_table, &cset->hlist, key); up_write(&css_set_rwsem); return cset; } static struct cgroup_root *cgroup_root_from_kf(struct kernfs_root *kf_root) { struct cgroup *root_cgrp = kf_root->kn->priv; return root_cgrp->root; } static int cgroup_init_root_id(struct cgroup_root *root) { int id; lockdep_assert_held(&cgroup_mutex); id = idr_alloc_cyclic(&cgroup_hierarchy_idr, root, 0, 0, GFP_KERNEL); if (id < 0) return id; root->hierarchy_id = id; return 0; } static void cgroup_exit_root_id(struct cgroup_root *root) { lockdep_assert_held(&cgroup_mutex); if (root->hierarchy_id) { idr_remove(&cgroup_hierarchy_idr, root->hierarchy_id); root->hierarchy_id = 0; } } static void cgroup_free_root(struct cgroup_root *root) { if (root) { /* hierarhcy ID shoulid already have been released */ WARN_ON_ONCE(root->hierarchy_id); idr_destroy(&root->cgroup_idr); kfree(root); } } static void cgroup_destroy_root(struct cgroup_root *root) { struct cgroup *cgrp = &root->cgrp; struct cgrp_cset_link *link, *tmp_link; mutex_lock(&cgroup_tree_mutex); mutex_lock(&cgroup_mutex); BUG_ON(atomic_read(&root->nr_cgrps)); BUG_ON(!list_empty(&cgrp->children)); /* Rebind all subsystems back to the default hierarchy */ rebind_subsystems(&cgrp_dfl_root, cgrp->subsys_mask); /* * Release all the links from cset_links to this hierarchy's * root cgroup */ down_write(&css_set_rwsem); list_for_each_entry_safe(link, tmp_link, &cgrp->cset_links, cset_link) { list_del(&link->cset_link); list_del(&link->cgrp_link); kfree(link); } up_write(&css_set_rwsem); if (!list_empty(&root->root_list)) { list_del(&root->root_list); cgroup_root_count--; } cgroup_exit_root_id(root); mutex_unlock(&cgroup_mutex); mutex_unlock(&cgroup_tree_mutex); kernfs_destroy_root(root->kf_root); cgroup_free_root(root); } /* look up cgroup associated with given css_set on the specified hierarchy */ static struct cgroup *cset_cgroup_from_root(struct css_set *cset, struct cgroup_root *root) { struct cgroup *res = NULL; lockdep_assert_held(&cgroup_mutex); lockdep_assert_held(&css_set_rwsem); if (cset == &init_css_set) { res = &root->cgrp; } else { struct cgrp_cset_link *link; list_for_each_entry(link, &cset->cgrp_links, cgrp_link) { struct cgroup *c = link->cgrp; if (c->root == root) { res = c; break; } } } BUG_ON(!res); return res; } /* * Return the cgroup for "task" from the given hierarchy. Must be * called with cgroup_mutex and css_set_rwsem held. */ static struct cgroup *task_cgroup_from_root(struct task_struct *task, struct cgroup_root *root) { /* * No need to lock the task - since we hold cgroup_mutex the * task can't change groups, so the only thing that can happen * is that it exits and its css is set back to init_css_set. */ return cset_cgroup_from_root(task_css_set(task), root); } /* * A task must hold cgroup_mutex to modify cgroups. * * Any task can increment and decrement the count field without lock. * So in general, code holding cgroup_mutex can't rely on the count * field not changing. However, if the count goes to zero, then only * cgroup_attach_task() can increment it again. Because a count of zero * means that no tasks are currently attached, therefore there is no * way a task attached to that cgroup can fork (the other way to * increment the count). So code holding cgroup_mutex can safely * assume that if the count is zero, it will stay zero. Similarly, if * a task holds cgroup_mutex on a cgroup with zero count, it * knows that the cgroup won't be removed, as cgroup_rmdir() * needs that mutex. * * The fork and exit callbacks cgroup_fork() and cgroup_exit(), don't * (usually) take cgroup_mutex. These are the two most performance * critical pieces of code here. The exception occurs on cgroup_exit(), * when a task in a notify_on_release cgroup exits. Then cgroup_mutex * is taken, and if the cgroup count is zero, a usermode call made * to the release agent with the name of the cgroup (path relative to * the root of cgroup file system) as the argument. * * A cgroup can only be deleted if both its 'count' of using tasks * is zero, and its list of 'children' cgroups is empty. Since all * tasks in the system use _some_ cgroup, and since there is always at * least one task in the system (init, pid == 1), therefore, root cgroup * always has either children cgroups and/or using tasks. So we don't * need a special hack to ensure that root cgroup cannot be deleted. * * P.S. One more locking exception. RCU is used to guard the * update of a tasks cgroup pointer by cgroup_attach_task() */ static int cgroup_populate_dir(struct cgroup *cgrp, unsigned long subsys_mask); static struct kernfs_syscall_ops cgroup_kf_syscall_ops; static const struct file_operations proc_cgroupstats_operations; static char *cgroup_file_name(struct cgroup *cgrp, const struct cftype *cft, char *buf) { if (cft->ss && !(cft->flags & CFTYPE_NO_PREFIX) && !(cgrp->root->flags & CGRP_ROOT_NOPREFIX)) snprintf(buf, CGROUP_FILE_NAME_MAX, "%s.%s", cft->ss->name, cft->name); else strncpy(buf, cft->name, CGROUP_FILE_NAME_MAX); return buf; } /** * cgroup_file_mode - deduce file mode of a control file * @cft: the control file in question * * returns cft->mode if ->mode is not 0 * returns S_IRUGO|S_IWUSR if it has both a read and a write handler * returns S_IRUGO if it has only a read handler * returns S_IWUSR if it has only a write hander */ static umode_t cgroup_file_mode(const struct cftype *cft) { umode_t mode = 0; if (cft->mode) return cft->mode; if (cft->read_u64 || cft->read_s64 || cft->seq_show) mode |= S_IRUGO; if (cft->write_u64 || cft->write_s64 || cft->write_string || cft->trigger) mode |= S_IWUSR; return mode; } static void cgroup_free_fn(struct work_struct *work) { struct cgroup *cgrp = container_of(work, struct cgroup, destroy_work); atomic_dec(&cgrp->root->nr_cgrps); cgroup_pidlist_destroy_all(cgrp); if (cgrp->parent) { /* * We get a ref to the parent, and put the ref when this * cgroup is being freed, so it's guaranteed that the * parent won't be destroyed before its children. */ cgroup_put(cgrp->parent); kernfs_put(cgrp->kn); kfree(cgrp); } else { /* * This is root cgroup's refcnt reaching zero, which * indicates that the root should be released. */ cgroup_destroy_root(cgrp->root); } } static void cgroup_free_rcu(struct rcu_head *head) { struct cgroup *cgrp = container_of(head, struct cgroup, rcu_head); INIT_WORK(&cgrp->destroy_work, cgroup_free_fn); queue_work(cgroup_destroy_wq, &cgrp->destroy_work); } static void cgroup_get(struct cgroup *cgrp) { WARN_ON_ONCE(cgroup_is_dead(cgrp)); WARN_ON_ONCE(atomic_read(&cgrp->refcnt) <= 0); atomic_inc(&cgrp->refcnt); } static void cgroup_put(struct cgroup *cgrp) { if (!atomic_dec_and_test(&cgrp->refcnt)) return; if (WARN_ON_ONCE(cgrp->parent && !cgroup_is_dead(cgrp))) return; /* * XXX: cgrp->id is only used to look up css's. As cgroup and * css's lifetimes will be decoupled, it should be made * per-subsystem and moved to css->id so that lookups are * successful until the target css is released. */ mutex_lock(&cgroup_mutex); idr_remove(&cgrp->root->cgroup_idr, cgrp->id); mutex_unlock(&cgroup_mutex); cgrp->id = -1; call_rcu(&cgrp->rcu_head, cgroup_free_rcu); } static void cgroup_rm_file(struct cgroup *cgrp, const struct cftype *cft) { char name[CGROUP_FILE_NAME_MAX]; lockdep_assert_held(&cgroup_tree_mutex); kernfs_remove_by_name(cgrp->kn, cgroup_file_name(cgrp, cft, name)); } /** * cgroup_clear_dir - remove subsys files in a cgroup directory * @cgrp: target cgroup * @subsys_mask: mask of the subsystem ids whose files should be removed */ static void cgroup_clear_dir(struct cgroup *cgrp, unsigned long subsys_mask) { struct cgroup_subsys *ss; int i; for_each_subsys(ss, i) { struct cftype *cfts; if (!test_bit(i, &subsys_mask)) continue; list_for_each_entry(cfts, &ss->cfts, node) cgroup_addrm_files(cgrp, cfts, false); } } static int rebind_subsystems(struct cgroup_root *dst_root, unsigned long ss_mask) { struct cgroup_subsys *ss; int ssid, ret; lockdep_assert_held(&cgroup_tree_mutex); lockdep_assert_held(&cgroup_mutex); for_each_subsys(ss, ssid) { if (!(ss_mask & (1 << ssid))) continue; /* if @ss is on the dummy_root, we can always move it */ if (ss->root == &cgrp_dfl_root) continue; /* if @ss has non-root cgroups attached to it, can't move */ if (!list_empty(&ss->root->cgrp.children)) return -EBUSY; /* can't move between two non-dummy roots either */ if (dst_root != &cgrp_dfl_root) return -EBUSY; } ret = cgroup_populate_dir(&dst_root->cgrp, ss_mask); if (ret) { if (dst_root != &cgrp_dfl_root) return ret; /* * Rebinding back to the default root is not allowed to * fail. Using both default and non-default roots should * be rare. Moving subsystems back and forth even more so. * Just warn about it and continue. */ if (cgrp_dfl_root_visible) { pr_warning("cgroup: failed to create files (%d) while rebinding 0x%lx to default root\n", ret, ss_mask); pr_warning("cgroup: you may retry by moving them to a different hierarchy and unbinding\n"); } } /* * Nothing can fail from this point on. Remove files for the * removed subsystems and rebind each subsystem. */ mutex_unlock(&cgroup_mutex); for_each_subsys(ss, ssid) if (ss_mask & (1 << ssid)) cgroup_clear_dir(&ss->root->cgrp, 1 << ssid); mutex_lock(&cgroup_mutex); for_each_subsys(ss, ssid) { struct cgroup_root *src_root; struct cgroup_subsys_state *css; if (!(ss_mask & (1 << ssid))) continue; src_root = ss->root; css = cgroup_css(&src_root->cgrp, ss); WARN_ON(!css || cgroup_css(&dst_root->cgrp, ss)); RCU_INIT_POINTER(src_root->cgrp.subsys[ssid], NULL); rcu_assign_pointer(dst_root->cgrp.subsys[ssid], css); ss->root = dst_root; css->cgroup = &dst_root->cgrp; src_root->cgrp.subsys_mask &= ~(1 << ssid); dst_root->cgrp.subsys_mask |= 1 << ssid; if (ss->bind) ss->bind(css); } kernfs_activate(dst_root->cgrp.kn); return 0; } static int cgroup_show_options(struct seq_file *seq, struct kernfs_root *kf_root) { struct cgroup_root *root = cgroup_root_from_kf(kf_root); struct cgroup_subsys *ss; int ssid; for_each_subsys(ss, ssid) if (root->cgrp.subsys_mask & (1 << ssid)) seq_printf(seq, ",%s", ss->name); if (root->flags & CGRP_ROOT_SANE_BEHAVIOR) seq_puts(seq, ",sane_behavior"); if (root->flags & CGRP_ROOT_NOPREFIX) seq_puts(seq, ",noprefix"); if (root->flags & CGRP_ROOT_XATTR) seq_puts(seq, ",xattr"); spin_lock(&release_agent_path_lock); if (strlen(root->release_agent_path)) seq_printf(seq, ",release_agent=%s", root->release_agent_path); spin_unlock(&release_agent_path_lock); if (test_bit(CGRP_CPUSET_CLONE_CHILDREN, &root->cgrp.flags)) seq_puts(seq, ",clone_children"); if (strlen(root->name)) seq_printf(seq, ",name=%s", root->name); return 0; } struct cgroup_sb_opts { unsigned long subsys_mask; unsigned long flags; char *release_agent; bool cpuset_clone_children; char *name; /* User explicitly requested empty subsystem */ bool none; }; /* * Convert a hierarchy specifier into a bitmask of subsystems and * flags. Call with cgroup_mutex held to protect the cgroup_subsys[] * array. This function takes refcounts on subsystems to be used, unless it * returns error, in which case no refcounts are taken. */ static int parse_cgroupfs_options(char *data, struct cgroup_sb_opts *opts) { char *token, *o = data; bool all_ss = false, one_ss = false; unsigned long mask = (unsigned long)-1; struct cgroup_subsys *ss; int i; BUG_ON(!mutex_is_locked(&cgroup_mutex)); #ifdef CONFIG_CPUSETS mask = ~(1UL << cpuset_cgrp_id); #endif memset(opts, 0, sizeof(*opts)); while ((token = strsep(&o, ",")) != NULL) { if (!*token) return -EINVAL; if (!strcmp(token, "none")) { /* Explicitly have no subsystems */ opts->none = true; continue; } if (!strcmp(token, "all")) { /* Mutually exclusive option 'all' + subsystem name */ if (one_ss) return -EINVAL; all_ss = true; continue; } if (!strcmp(token, "__DEVEL__sane_behavior")) { opts->flags |= CGRP_ROOT_SANE_BEHAVIOR; continue; } if (!strcmp(token, "noprefix")) { opts->flags |= CGRP_ROOT_NOPREFIX; continue; } if (!strcmp(token, "clone_children")) { opts->cpuset_clone_children = true; continue; } if (!strcmp(token, "xattr")) { opts->flags |= CGRP_ROOT_XATTR; continue; } if (!strncmp(token, "release_agent=", 14)) { /* Specifying two release agents is forbidden */ if (opts->release_agent) return -EINVAL; opts->release_agent = kstrndup(token + 14, PATH_MAX - 1, GFP_KERNEL); if (!opts->release_agent) return -ENOMEM; continue; } if (!strncmp(token, "name=", 5)) { const char *name = token + 5; /* Can't specify an empty name */ if (!strlen(name)) return -EINVAL; /* Must match [\w.-]+ */ for (i = 0; i < strlen(name); i++) { char c = name[i]; if (isalnum(c)) continue; if ((c == '.') || (c == '-') || (c == '_')) continue; return -EINVAL; } /* Specifying two names is forbidden */ if (opts->name) return -EINVAL; opts->name = kstrndup(name, MAX_CGROUP_ROOT_NAMELEN - 1, GFP_KERNEL); if (!opts->name) return -ENOMEM; continue; } for_each_subsys(ss, i) { if (strcmp(token, ss->name)) continue; if (ss->disabled) continue; /* Mutually exclusive option 'all' + subsystem name */ if (all_ss) return -EINVAL; set_bit(i, &opts->subsys_mask); one_ss = true; break; } if (i == CGROUP_SUBSYS_COUNT) return -ENOENT; } /* Consistency checks */ if (opts->flags & CGRP_ROOT_SANE_BEHAVIOR) { pr_warning("cgroup: sane_behavior: this is still under development and its behaviors will change, proceed at your own risk\n"); if ((opts->flags & (CGRP_ROOT_NOPREFIX | CGRP_ROOT_XATTR)) || opts->cpuset_clone_children || opts->release_agent || opts->name) { pr_err("cgroup: sane_behavior: noprefix, xattr, clone_children, release_agent and name are not allowed\n"); return -EINVAL; } } else { /* * If the 'all' option was specified select all the * subsystems, otherwise if 'none', 'name=' and a subsystem * name options were not specified, let's default to 'all' */ if (all_ss || (!one_ss && !opts->none && !opts->name)) for_each_subsys(ss, i) if (!ss->disabled) set_bit(i, &opts->subsys_mask); /* * We either have to specify by name or by subsystems. (So * all empty hierarchies must have a name). */ if (!opts->subsys_mask && !opts->name) return -EINVAL; } /* * Option noprefix was introduced just for backward compatibility * with the old cpuset, so we allow noprefix only if mounting just * the cpuset subsystem. */ if ((opts->flags & CGRP_ROOT_NOPREFIX) && (opts->subsys_mask & mask)) return -EINVAL; /* Can't specify "none" and some subsystems */ if (opts->subsys_mask && opts->none) return -EINVAL; return 0; } static int cgroup_remount(struct kernfs_root *kf_root, int *flags, char *data) { int ret = 0; struct cgroup_root *root = cgroup_root_from_kf(kf_root); struct cgroup_sb_opts opts; unsigned long added_mask, removed_mask; if (root->flags & CGRP_ROOT_SANE_BEHAVIOR) { pr_err("cgroup: sane_behavior: remount is not allowed\n"); return -EINVAL; } mutex_lock(&cgroup_tree_mutex); mutex_lock(&cgroup_mutex); /* See what subsystems are wanted */ ret = parse_cgroupfs_options(data, &opts); if (ret) goto out_unlock; if (opts.subsys_mask != root->cgrp.subsys_mask || opts.release_agent) pr_warning("cgroup: option changes via remount are deprecated (pid=%d comm=%s)\n", task_tgid_nr(current), current->comm); added_mask = opts.subsys_mask & ~root->cgrp.subsys_mask; removed_mask = root->cgrp.subsys_mask & ~opts.subsys_mask; /* Don't allow flags or name to change at remount */ if (((opts.flags ^ root->flags) & CGRP_ROOT_OPTION_MASK) || (opts.name && strcmp(opts.name, root->name))) { pr_err("cgroup: option or name mismatch, new: 0x%lx \"%s\", old: 0x%lx \"%s\"\n", opts.flags & CGRP_ROOT_OPTION_MASK, opts.name ?: "", root->flags & CGRP_ROOT_OPTION_MASK, root->name); ret = -EINVAL; goto out_unlock; } /* remounting is not allowed for populated hierarchies */ if (!list_empty(&root->cgrp.children)) { ret = -EBUSY; goto out_unlock; } ret = rebind_subsystems(root, added_mask); if (ret) goto out_unlock; rebind_subsystems(&cgrp_dfl_root, removed_mask); if (opts.release_agent) { spin_lock(&release_agent_path_lock); strcpy(root->release_agent_path, opts.release_agent); spin_unlock(&release_agent_path_lock); } out_unlock: kfree(opts.release_agent); kfree(opts.name); mutex_unlock(&cgroup_mutex); mutex_unlock(&cgroup_tree_mutex); return ret; } /* * To reduce the fork() overhead for systems that are not actually using * their cgroups capability, we don't maintain the lists running through * each css_set to its tasks until we see the list actually used - in other * words after the first mount. */ static bool use_task_css_set_links __read_mostly; static void cgroup_enable_task_cg_lists(void) { struct task_struct *p, *g; down_write(&css_set_rwsem); if (use_task_css_set_links) goto out_unlock; use_task_css_set_links = true; /* * We need tasklist_lock because RCU is not safe against * while_each_thread(). Besides, a forking task that has passed * cgroup_post_fork() without seeing use_task_css_set_links = 1 * is not guaranteed to have its child immediately visible in the * tasklist if we walk through it with RCU. */ read_lock(&tasklist_lock); do_each_thread(g, p) { WARN_ON_ONCE(!list_empty(&p->cg_list) || task_css_set(p) != &init_css_set); /* * We should check if the process is exiting, otherwise * it will race with cgroup_exit() in that the list * entry won't be deleted though the process has exited. * Do it while holding siglock so that we don't end up * racing against cgroup_exit(). */ spin_lock_irq(&p->sighand->siglock); if (!(p->flags & PF_EXITING)) { struct css_set *cset = task_css_set(p); list_add(&p->cg_list, &cset->tasks); get_css_set(cset); } spin_unlock_irq(&p->sighand->siglock); } while_each_thread(g, p); read_unlock(&tasklist_lock); out_unlock: up_write(&css_set_rwsem); } static void init_cgroup_housekeeping(struct cgroup *cgrp) { atomic_set(&cgrp->refcnt, 1); INIT_LIST_HEAD(&cgrp->sibling); INIT_LIST_HEAD(&cgrp->children); INIT_LIST_HEAD(&cgrp->cset_links); INIT_LIST_HEAD(&cgrp->release_list); INIT_LIST_HEAD(&cgrp->pidlists); mutex_init(&cgrp->pidlist_mutex); cgrp->dummy_css.cgroup = cgrp; } static void init_cgroup_root(struct cgroup_root *root, struct cgroup_sb_opts *opts) { struct cgroup *cgrp = &root->cgrp; INIT_LIST_HEAD(&root->root_list); atomic_set(&root->nr_cgrps, 1); cgrp->root = root; init_cgroup_housekeeping(cgrp); idr_init(&root->cgroup_idr); root->flags = opts->flags; if (opts->release_agent) strcpy(root->release_agent_path, opts->release_agent); if (opts->name) strcpy(root->name, opts->name); if (opts->cpuset_clone_children) set_bit(CGRP_CPUSET_CLONE_CHILDREN, &root->cgrp.flags); } static int cgroup_setup_root(struct cgroup_root *root, unsigned long ss_mask) { LIST_HEAD(tmp_links); struct cgroup *root_cgrp = &root->cgrp; struct css_set *cset; int i, ret; lockdep_assert_held(&cgroup_tree_mutex); lockdep_assert_held(&cgroup_mutex); ret = idr_alloc(&root->cgroup_idr, root_cgrp, 0, 1, GFP_KERNEL); if (ret < 0) goto out; root_cgrp->id = ret; /* * We're accessing css_set_count without locking css_set_rwsem here, * but that's OK - it can only be increased by someone holding * cgroup_lock, and that's us. The worst that can happen is that we * have some link structures left over */ ret = allocate_cgrp_cset_links(css_set_count, &tmp_links); if (ret) goto out; ret = cgroup_init_root_id(root); if (ret) goto out; root->kf_root = kernfs_create_root(&cgroup_kf_syscall_ops, KERNFS_ROOT_CREATE_DEACTIVATED, root_cgrp); if (IS_ERR(root->kf_root)) { ret = PTR_ERR(root->kf_root); goto exit_root_id; } root_cgrp->kn = root->kf_root->kn; ret = cgroup_addrm_files(root_cgrp, cgroup_base_files, true); if (ret) goto destroy_root; ret = rebind_subsystems(root, ss_mask); if (ret) goto destroy_root; /* * There must be no failure case after here, since rebinding takes * care of subsystems' refcounts, which are explicitly dropped in * the failure exit path. */ list_add(&root->root_list, &cgroup_roots); cgroup_root_count++; /* * Link the root cgroup in this hierarchy into all the css_set * objects. */ down_write(&css_set_rwsem); hash_for_each(css_set_table, i, cset, hlist) link_css_set(&tmp_links, cset, root_cgrp); up_write(&css_set_rwsem); BUG_ON(!list_empty(&root_cgrp->children)); BUG_ON(atomic_read(&root->nr_cgrps) != 1); kernfs_activate(root_cgrp->kn); ret = 0; goto out; destroy_root: kernfs_destroy_root(root->kf_root); root->kf_root = NULL; exit_root_id: cgroup_exit_root_id(root); out: free_cgrp_cset_links(&tmp_links); return ret; } static struct dentry *cgroup_mount(struct file_system_type *fs_type, int flags, const char *unused_dev_name, void *data) { struct cgroup_root *root; struct cgroup_sb_opts opts; struct dentry *dentry; int ret; /* * The first time anyone tries to mount a cgroup, enable the list * linking each css_set to its tasks and fix up all existing tasks. */ if (!use_task_css_set_links) cgroup_enable_task_cg_lists(); retry: mutex_lock(&cgroup_tree_mutex); mutex_lock(&cgroup_mutex); /* First find the desired set of subsystems */ ret = parse_cgroupfs_options(data, &opts); if (ret) goto out_unlock; /* look for a matching existing root */ if (!opts.subsys_mask && !opts.none && !opts.name) { cgrp_dfl_root_visible = true; root = &cgrp_dfl_root; cgroup_get(&root->cgrp); ret = 0; goto out_unlock; } for_each_root(root) { bool name_match = false; if (root == &cgrp_dfl_root) continue; /* * If we asked for a name then it must match. Also, if * name matches but sybsys_mask doesn't, we should fail. * Remember whether name matched. */ if (opts.name) { if (strcmp(opts.name, root->name)) continue; name_match = true; } /* * If we asked for subsystems (or explicitly for no * subsystems) then they must match. */ if ((opts.subsys_mask || opts.none) && (opts.subsys_mask != root->cgrp.subsys_mask)) { if (!name_match) continue; ret = -EBUSY; goto out_unlock; } if ((root->flags ^ opts.flags) & CGRP_ROOT_OPTION_MASK) { if ((root->flags | opts.flags) & CGRP_ROOT_SANE_BEHAVIOR) { pr_err("cgroup: sane_behavior: new mount options should match the existing superblock\n"); ret = -EINVAL; goto out_unlock; } else { pr_warning("cgroup: new mount options do not match the existing superblock, will be ignored\n"); } } /* * A root's lifetime is governed by its root cgroup. Zero * ref indicate that the root is being destroyed. Wait for * destruction to complete so that the subsystems are free. * We can use wait_queue for the wait but this path is * super cold. Let's just sleep for a bit and retry. */ if (!atomic_inc_not_zero(&root->cgrp.refcnt)) { mutex_unlock(&cgroup_mutex); mutex_unlock(&cgroup_tree_mutex); kfree(opts.release_agent); kfree(opts.name); msleep(10); goto retry; } ret = 0; goto out_unlock; } /* * No such thing, create a new one. name= matching without subsys * specification is allowed for already existing hierarchies but we * can't create new one without subsys specification. */ if (!opts.subsys_mask && !opts.none) { ret = -EINVAL; goto out_unlock; } root = kzalloc(sizeof(*root), GFP_KERNEL); if (!root) { ret = -ENOMEM; goto out_unlock; } init_cgroup_root(root, &opts); ret = cgroup_setup_root(root, opts.subsys_mask); if (ret) cgroup_free_root(root); out_unlock: mutex_unlock(&cgroup_mutex); mutex_unlock(&cgroup_tree_mutex); kfree(opts.release_agent); kfree(opts.name); if (ret) return ERR_PTR(ret); dentry = kernfs_mount(fs_type, flags, root->kf_root); if (IS_ERR(dentry)) cgroup_put(&root->cgrp); return dentry; } static void cgroup_kill_sb(struct super_block *sb) { struct kernfs_root *kf_root = kernfs_root_from_sb(sb); struct cgroup_root *root = cgroup_root_from_kf(kf_root); cgroup_put(&root->cgrp); kernfs_kill_sb(sb); } static struct file_system_type cgroup_fs_type = { .name = "cgroup", .mount = cgroup_mount, .kill_sb = cgroup_kill_sb, }; static struct kobject *cgroup_kobj; /** * task_cgroup_path - cgroup path of a task in the first cgroup hierarchy * @task: target task * @buf: the buffer to write the path into * @buflen: the length of the buffer * * Determine @task's cgroup on the first (the one with the lowest non-zero * hierarchy_id) cgroup hierarchy and copy its path into @buf. This * function grabs cgroup_mutex and shouldn't be used inside locks used by * cgroup controller callbacks. * * Return value is the same as kernfs_path(). */ char *task_cgroup_path(struct task_struct *task, char *buf, size_t buflen) { struct cgroup_root *root; struct cgroup *cgrp; int hierarchy_id = 1; char *path = NULL; mutex_lock(&cgroup_mutex); down_read(&css_set_rwsem); root = idr_get_next(&cgroup_hierarchy_idr, &hierarchy_id); if (root) { cgrp = task_cgroup_from_root(task, root); path = cgroup_path(cgrp, buf, buflen); } else { /* if no hierarchy exists, everyone is in "/" */ if (strlcpy(buf, "/", buflen) < buflen) path = buf; } up_read(&css_set_rwsem); mutex_unlock(&cgroup_mutex); return path; } EXPORT_SYMBOL_GPL(task_cgroup_path); /* used to track tasks and other necessary states during migration */ struct cgroup_taskset { /* the src and dst cset list running through cset->mg_node */ struct list_head src_csets; struct list_head dst_csets; /* * Fields for cgroup_taskset_*() iteration. * * Before migration is committed, the target migration tasks are on * ->mg_tasks of the csets on ->src_csets. After, on ->mg_tasks of * the csets on ->dst_csets. ->csets point to either ->src_csets * or ->dst_csets depending on whether migration is committed. * * ->cur_csets and ->cur_task point to the current task position * during iteration. */ struct list_head *csets; struct css_set *cur_cset; struct task_struct *cur_task; }; /** * cgroup_taskset_first - reset taskset and return the first task * @tset: taskset of interest * * @tset iteration is initialized and the first task is returned. */ struct task_struct *cgroup_taskset_first(struct cgroup_taskset *tset) { tset->cur_cset = list_first_entry(tset->csets, struct css_set, mg_node); tset->cur_task = NULL; return cgroup_taskset_next(tset); } /** * cgroup_taskset_next - iterate to the next task in taskset * @tset: taskset of interest * * Return the next task in @tset. Iteration must have been initialized * with cgroup_taskset_first(). */ struct task_struct *cgroup_taskset_next(struct cgroup_taskset *tset) { struct css_set *cset = tset->cur_cset; struct task_struct *task = tset->cur_task; while (&cset->mg_node != tset->csets) { if (!task) task = list_first_entry(&cset->mg_tasks, struct task_struct, cg_list); else task = list_next_entry(task, cg_list); if (&task->cg_list != &cset->mg_tasks) { tset->cur_cset = cset; tset->cur_task = task; return task; } cset = list_next_entry(cset, mg_node); task = NULL; } return NULL; } /** * cgroup_task_migrate - move a task from one cgroup to another. * @old_cgrp; the cgroup @tsk is being migrated from * @tsk: the task being migrated * @new_cset: the new css_set @tsk is being attached to * * Must be called with cgroup_mutex, threadgroup and css_set_rwsem locked. */ static void cgroup_task_migrate(struct cgroup *old_cgrp, struct task_struct *tsk, struct css_set *new_cset) { struct css_set *old_cset; lockdep_assert_held(&cgroup_mutex); lockdep_assert_held(&css_set_rwsem); /* * We are synchronized through threadgroup_lock() against PF_EXITING * setting such that we can't race against cgroup_exit() changing the * css_set to init_css_set and dropping the old one. */ WARN_ON_ONCE(tsk->flags & PF_EXITING); old_cset = task_css_set(tsk); get_css_set(new_cset); rcu_assign_pointer(tsk->cgroups, new_cset); /* * Use move_tail so that cgroup_taskset_first() still returns the * leader after migration. This works because cgroup_migrate() * ensures that the dst_cset of the leader is the first on the * tset's dst_csets list. */ list_move_tail(&tsk->cg_list, &new_cset->mg_tasks); /* * We just gained a reference on old_cset by taking it from the * task. As trading it for new_cset is protected by cgroup_mutex, * we're safe to drop it here; it will be freed under RCU. */ set_bit(CGRP_RELEASABLE, &old_cgrp->flags); put_css_set_locked(old_cset, false); } /** * cgroup_migrate_finish - cleanup after attach * @preloaded_csets: list of preloaded css_sets * * Undo cgroup_migrate_add_src() and cgroup_migrate_prepare_dst(). See * those functions for details. */ static void cgroup_migrate_finish(struct list_head *preloaded_csets) { struct css_set *cset, *tmp_cset; lockdep_assert_held(&cgroup_mutex); down_write(&css_set_rwsem); list_for_each_entry_safe(cset, tmp_cset, preloaded_csets, mg_preload_node) { cset->mg_src_cgrp = NULL; cset->mg_dst_cset = NULL; list_del_init(&cset->mg_preload_node); put_css_set_locked(cset, false); } up_write(&css_set_rwsem); } /** * cgroup_migrate_add_src - add a migration source css_set * @src_cset: the source css_set to add * @dst_cgrp: the destination cgroup * @preloaded_csets: list of preloaded css_sets * * Tasks belonging to @src_cset are about to be migrated to @dst_cgrp. Pin * @src_cset and add it to @preloaded_csets, which should later be cleaned * up by cgroup_migrate_finish(). * * This function may be called without holding threadgroup_lock even if the * target is a process. Threads may be created and destroyed but as long * as cgroup_mutex is not dropped, no new css_set can be put into play and * the preloaded css_sets are guaranteed to cover all migrations. */ static void cgroup_migrate_add_src(struct css_set *src_cset, struct cgroup *dst_cgrp, struct list_head *preloaded_csets) { struct cgroup *src_cgrp; lockdep_assert_held(&cgroup_mutex); lockdep_assert_held(&css_set_rwsem); src_cgrp = cset_cgroup_from_root(src_cset, dst_cgrp->root); /* nothing to do if this cset already belongs to the cgroup */ if (src_cgrp == dst_cgrp) return; if (!list_empty(&src_cset->mg_preload_node)) return; WARN_ON(src_cset->mg_src_cgrp); WARN_ON(!list_empty(&src_cset->mg_tasks)); WARN_ON(!list_empty(&src_cset->mg_node)); src_cset->mg_src_cgrp = src_cgrp; get_css_set(src_cset); list_add(&src_cset->mg_preload_node, preloaded_csets); } /** * cgroup_migrate_prepare_dst - prepare destination css_sets for migration * @dst_cgrp: the destination cgroup * @preloaded_csets: list of preloaded source css_sets * * Tasks are about to be moved to @dst_cgrp and all the source css_sets * have been preloaded to @preloaded_csets. This function looks up and * pins all destination css_sets, links each to its source, and put them on * @preloaded_csets. * * This function must be called after cgroup_migrate_add_src() has been * called on each migration source css_set. After migration is performed * using cgroup_migrate(), cgroup_migrate_finish() must be called on * @preloaded_csets. */ static int cgroup_migrate_prepare_dst(struct cgroup *dst_cgrp, struct list_head *preloaded_csets) { LIST_HEAD(csets); struct css_set *src_cset; lockdep_assert_held(&cgroup_mutex); /* look up the dst cset for each src cset and link it to src */ list_for_each_entry(src_cset, preloaded_csets, mg_preload_node) { struct css_set *dst_cset; dst_cset = find_css_set(src_cset, dst_cgrp); if (!dst_cset) goto err; WARN_ON_ONCE(src_cset->mg_dst_cset || dst_cset->mg_dst_cset); src_cset->mg_dst_cset = dst_cset; if (list_empty(&dst_cset->mg_preload_node)) list_add(&dst_cset->mg_preload_node, &csets); else put_css_set(dst_cset, false); } list_splice(&csets, preloaded_csets); return 0; err: cgroup_migrate_finish(&csets); return -ENOMEM; } /** * cgroup_migrate - migrate a process or task to a cgroup * @cgrp: the destination cgroup * @leader: the leader of the process or the task to migrate * @threadgroup: whether @leader points to the whole process or a single task * * Migrate a process or task denoted by @leader to @cgrp. If migrating a * process, the caller must be holding threadgroup_lock of @leader. The * caller is also responsible for invoking cgroup_migrate_add_src() and * cgroup_migrate_prepare_dst() on the targets before invoking this * function and following up with cgroup_migrate_finish(). * * As long as a controller's ->can_attach() doesn't fail, this function is * guaranteed to succeed. This means that, excluding ->can_attach() * failure, when migrating multiple targets, the success or failure can be * decided for all targets by invoking group_migrate_prepare_dst() before * actually starting migrating. */ static int cgroup_migrate(struct cgroup *cgrp, struct task_struct *leader, bool threadgroup) { struct cgroup_taskset tset = { .src_csets = LIST_HEAD_INIT(tset.src_csets), .dst_csets = LIST_HEAD_INIT(tset.dst_csets), .csets = &tset.src_csets, }; struct cgroup_subsys_state *css, *failed_css = NULL; struct css_set *cset, *tmp_cset; struct task_struct *task, *tmp_task; int i, ret; /* * Prevent freeing of tasks while we take a snapshot. Tasks that are * already PF_EXITING could be freed from underneath us unless we * take an rcu_read_lock. */ down_write(&css_set_rwsem); rcu_read_lock(); task = leader; do { /* @task either already exited or can't exit until the end */ if (task->flags & PF_EXITING) goto next; /* leave @task alone if post_fork() hasn't linked it yet */ if (list_empty(&task->cg_list)) goto next; cset = task_css_set(task); if (!cset->mg_src_cgrp) goto next; /* * cgroup_taskset_first() must always return the leader. * Take care to avoid disturbing the ordering. */ list_move_tail(&task->cg_list, &cset->mg_tasks); if (list_empty(&cset->mg_node)) list_add_tail(&cset->mg_node, &tset.src_csets); if (list_empty(&cset->mg_dst_cset->mg_node)) list_move_tail(&cset->mg_dst_cset->mg_node, &tset.dst_csets); next: if (!threadgroup) break; } while_each_thread(leader, task); rcu_read_unlock(); up_write(&css_set_rwsem); /* methods shouldn't be called if no task is actually migrating */ if (list_empty(&tset.src_csets)) return 0; /* check that we can legitimately attach to the cgroup */ for_each_css(css, i, cgrp) { if (css->ss->can_attach) { ret = css->ss->can_attach(css, &tset); if (ret) { failed_css = css; goto out_cancel_attach; } } } /* * Now that we're guaranteed success, proceed to move all tasks to * the new cgroup. There are no failure cases after here, so this * is the commit point. */ down_write(&css_set_rwsem); list_for_each_entry(cset, &tset.src_csets, mg_node) { list_for_each_entry_safe(task, tmp_task, &cset->mg_tasks, cg_list) cgroup_task_migrate(cset->mg_src_cgrp, task, cset->mg_dst_cset); } up_write(&css_set_rwsem); /* * Migration is committed, all target tasks are now on dst_csets. * Nothing is sensitive to fork() after this point. Notify * controllers that migration is complete. */ tset.csets = &tset.dst_csets; for_each_css(css, i, cgrp) if (css->ss->attach) css->ss->attach(css, &tset); ret = 0; goto out_release_tset; out_cancel_attach: for_each_css(css, i, cgrp) { if (css == failed_css) break; if (css->ss->cancel_attach) css->ss->cancel_attach(css, &tset); } out_release_tset: down_write(&css_set_rwsem); list_splice_init(&tset.dst_csets, &tset.src_csets); list_for_each_entry_safe(cset, tmp_cset, &tset.src_csets, mg_node) { list_splice_tail_init(&cset->mg_tasks, &cset->tasks); list_del_init(&cset->mg_node); } up_write(&css_set_rwsem); return ret; } /** * cgroup_attach_task - attach a task or a whole threadgroup to a cgroup * @dst_cgrp: the cgroup to attach to * @leader: the task or the leader of the threadgroup to be attached * @threadgroup: attach the whole threadgroup? * * Call holding cgroup_mutex and threadgroup_lock of @leader. */ static int cgroup_attach_task(struct cgroup *dst_cgrp, struct task_struct *leader, bool threadgroup) { LIST_HEAD(preloaded_csets); struct task_struct *task; int ret; /* look up all src csets */ down_read(&css_set_rwsem); rcu_read_lock(); task = leader; do { cgroup_migrate_add_src(task_css_set(task), dst_cgrp, &preloaded_csets); if (!threadgroup) break; } while_each_thread(leader, task); rcu_read_unlock(); up_read(&css_set_rwsem); /* prepare dst csets and commit */ ret = cgroup_migrate_prepare_dst(dst_cgrp, &preloaded_csets); if (!ret) ret = cgroup_migrate(dst_cgrp, leader, threadgroup); cgroup_migrate_finish(&preloaded_csets); return ret; } /* * Find the task_struct of the task to attach by vpid and pass it along to the * function to attach either it or all tasks in its threadgroup. Will lock * cgroup_mutex and threadgroup. */ static int attach_task_by_pid(struct cgroup *cgrp, u64 pid, bool threadgroup) { struct task_struct *tsk; const struct cred *cred = current_cred(), *tcred; int ret; if (!cgroup_lock_live_group(cgrp)) return -ENODEV; retry_find_task: rcu_read_lock(); if (pid) { tsk = find_task_by_vpid(pid); if (!tsk) { rcu_read_unlock(); ret = -ESRCH; goto out_unlock_cgroup; } /* * even if we're attaching all tasks in the thread group, we * only need to check permissions on one of them. */ tcred = __task_cred(tsk); if (!uid_eq(cred->euid, GLOBAL_ROOT_UID) && !uid_eq(cred->euid, tcred->uid) && !uid_eq(cred->euid, tcred->suid)) { rcu_read_unlock(); ret = -EACCES; goto out_unlock_cgroup; } } else tsk = current; if (threadgroup) tsk = tsk->group_leader; /* * Workqueue threads may acquire PF_NO_SETAFFINITY and become * trapped in a cpuset, or RT worker may be born in a cgroup * with no rt_runtime allocated. Just say no. */ if (tsk == kthreadd_task || (tsk->flags & PF_NO_SETAFFINITY)) { ret = -EINVAL; rcu_read_unlock(); goto out_unlock_cgroup; } get_task_struct(tsk); rcu_read_unlock(); threadgroup_lock(tsk); if (threadgroup) { if (!thread_group_leader(tsk)) { /* * a race with de_thread from another thread's exec() * may strip us of our leadership, if this happens, * there is no choice but to throw this task away and * try again; this is * "double-double-toil-and-trouble-check locking". */ threadgroup_unlock(tsk); put_task_struct(tsk); goto retry_find_task; } } ret = cgroup_attach_task(cgrp, tsk, threadgroup); threadgroup_unlock(tsk); put_task_struct(tsk); out_unlock_cgroup: mutex_unlock(&cgroup_mutex); return ret; } /** * cgroup_attach_task_all - attach task 'tsk' to all cgroups of task 'from' * @from: attach to all cgroups of a given task * @tsk: the task to be attached */ int cgroup_attach_task_all(struct task_struct *from, struct task_struct *tsk) { struct cgroup_root *root; int retval = 0; mutex_lock(&cgroup_mutex); for_each_root(root) { struct cgroup *from_cgrp; if (root == &cgrp_dfl_root) continue; down_read(&css_set_rwsem); from_cgrp = task_cgroup_from_root(from, root); up_read(&css_set_rwsem); retval = cgroup_attach_task(from_cgrp, tsk, false); if (retval) break; } mutex_unlock(&cgroup_mutex); return retval; } EXPORT_SYMBOL_GPL(cgroup_attach_task_all); static int cgroup_tasks_write(struct cgroup_subsys_state *css, struct cftype *cft, u64 pid) { return attach_task_by_pid(css->cgroup, pid, false); } static int cgroup_procs_write(struct cgroup_subsys_state *css, struct cftype *cft, u64 tgid) { return attach_task_by_pid(css->cgroup, tgid, true); } static int cgroup_release_agent_write(struct cgroup_subsys_state *css, struct cftype *cft, char *buffer) { struct cgroup_root *root = css->cgroup->root; BUILD_BUG_ON(sizeof(root->release_agent_path) < PATH_MAX); if (!cgroup_lock_live_group(css->cgroup)) return -ENODEV; spin_lock(&release_agent_path_lock); strlcpy(root->release_agent_path, buffer, sizeof(root->release_agent_path)); spin_unlock(&release_agent_path_lock); mutex_unlock(&cgroup_mutex); return 0; } static int cgroup_release_agent_show(struct seq_file *seq, void *v) { struct cgroup *cgrp = seq_css(seq)->cgroup; if (!cgroup_lock_live_group(cgrp)) return -ENODEV; seq_puts(seq, cgrp->root->release_agent_path); seq_putc(seq, '\n'); mutex_unlock(&cgroup_mutex); return 0; } static int cgroup_sane_behavior_show(struct seq_file *seq, void *v) { struct cgroup *cgrp = seq_css(seq)->cgroup; seq_printf(seq, "%d\n", cgroup_sane_behavior(cgrp)); return 0; } static ssize_t cgroup_file_write(struct kernfs_open_file *of, char *buf, size_t nbytes, loff_t off) { struct cgroup *cgrp = of->kn->parent->priv; struct cftype *cft = of->kn->priv; struct cgroup_subsys_state *css; int ret; /* * kernfs guarantees that a file isn't deleted with operations in * flight, which means that the matching css is and stays alive and * doesn't need to be pinned. The RCU locking is not necessary * either. It's just for the convenience of using cgroup_css(). */ rcu_read_lock(); css = cgroup_css(cgrp, cft->ss); rcu_read_unlock(); if (cft->write_string) { ret = cft->write_string(css, cft, strstrip(buf)); } else if (cft->write_u64) { unsigned long long v; ret = kstrtoull(buf, 0, &v); if (!ret) ret = cft->write_u64(css, cft, v); } else if (cft->write_s64) { long long v; ret = kstrtoll(buf, 0, &v); if (!ret) ret = cft->write_s64(css, cft, v); } else if (cft->trigger) { ret = cft->trigger(css, (unsigned int)cft->private); } else { ret = -EINVAL; } return ret ?: nbytes; } static void *cgroup_seqfile_start(struct seq_file *seq, loff_t *ppos) { return seq_cft(seq)->seq_start(seq, ppos); } static void *cgroup_seqfile_next(struct seq_file *seq, void *v, loff_t *ppos) { return seq_cft(seq)->seq_next(seq, v, ppos); } static void cgroup_seqfile_stop(struct seq_file *seq, void *v) { seq_cft(seq)->seq_stop(seq, v); } static int cgroup_seqfile_show(struct seq_file *m, void *arg) { struct cftype *cft = seq_cft(m); struct cgroup_subsys_state *css = seq_css(m); if (cft->seq_show) return cft->seq_show(m, arg); if (cft->read_u64) seq_printf(m, "%llu\n", cft->read_u64(css, cft)); else if (cft->read_s64) seq_printf(m, "%lld\n", cft->read_s64(css, cft)); else return -EINVAL; return 0; } static struct kernfs_ops cgroup_kf_single_ops = { .atomic_write_len = PAGE_SIZE, .write = cgroup_file_write, .seq_show = cgroup_seqfile_show, }; static struct kernfs_ops cgroup_kf_ops = { .atomic_write_len = PAGE_SIZE, .write = cgroup_file_write, .seq_start = cgroup_seqfile_start, .seq_next = cgroup_seqfile_next, .seq_stop = cgroup_seqfile_stop, .seq_show = cgroup_seqfile_show, }; /* * cgroup_rename - Only allow simple rename of directories in place. */ static int cgroup_rename(struct kernfs_node *kn, struct kernfs_node *new_parent, const char *new_name_str) { struct cgroup *cgrp = kn->priv; int ret; if (kernfs_type(kn) != KERNFS_DIR) return -ENOTDIR; if (kn->parent != new_parent) return -EIO; /* * This isn't a proper migration and its usefulness is very * limited. Disallow if sane_behavior. */ if (cgroup_sane_behavior(cgrp)) return -EPERM; mutex_lock(&cgroup_tree_mutex); mutex_lock(&cgroup_mutex); ret = kernfs_rename(kn, new_parent, new_name_str); mutex_unlock(&cgroup_mutex); mutex_unlock(&cgroup_tree_mutex); return ret; } static int cgroup_add_file(struct cgroup *cgrp, struct cftype *cft) { char name[CGROUP_FILE_NAME_MAX]; struct kernfs_node *kn; struct lock_class_key *key = NULL; #ifdef CONFIG_DEBUG_LOCK_ALLOC key = &cft->lockdep_key; #endif kn = __kernfs_create_file(cgrp->kn, cgroup_file_name(cgrp, cft, name), cgroup_file_mode(cft), 0, cft->kf_ops, cft, NULL, false, key); return PTR_ERR_OR_ZERO(kn); } /** * cgroup_addrm_files - add or remove files to a cgroup directory * @cgrp: the target cgroup * @cfts: array of cftypes to be added * @is_add: whether to add or remove * * Depending on @is_add, add or remove files defined by @cfts on @cgrp. * For removals, this function never fails. If addition fails, this * function doesn't remove files already added. The caller is responsible * for cleaning up. */ static int cgroup_addrm_files(struct cgroup *cgrp, struct cftype cfts[], bool is_add) { struct cftype *cft; int ret; lockdep_assert_held(&cgroup_tree_mutex); for (cft = cfts; cft->name[0] != '\0'; cft++) { /* does cft->flags tell us to skip this file on @cgrp? */ if ((cft->flags & CFTYPE_ONLY_ON_DFL) && !cgroup_on_dfl(cgrp)) continue; if ((cft->flags & CFTYPE_INSANE) && cgroup_sane_behavior(cgrp)) continue; if ((cft->flags & CFTYPE_NOT_ON_ROOT) && !cgrp->parent) continue; if ((cft->flags & CFTYPE_ONLY_ON_ROOT) && cgrp->parent) continue; if (is_add) { ret = cgroup_add_file(cgrp, cft); if (ret) { pr_warn("cgroup_addrm_files: failed to add %s, err=%d\n", cft->name, ret); return ret; } } else { cgroup_rm_file(cgrp, cft); } } return 0; } static int cgroup_apply_cftypes(struct cftype *cfts, bool is_add) { LIST_HEAD(pending); struct cgroup_subsys *ss = cfts[0].ss; struct cgroup *root = &ss->root->cgrp; struct cgroup_subsys_state *css; int ret = 0; lockdep_assert_held(&cgroup_tree_mutex); /* don't bother if @ss isn't attached */ if (ss->root == &cgrp_dfl_root) return 0; /* add/rm files for all cgroups created before */ css_for_each_descendant_pre(css, cgroup_css(root, ss)) { struct cgroup *cgrp = css->cgroup; if (cgroup_is_dead(cgrp)) continue; ret = cgroup_addrm_files(cgrp, cfts, is_add); if (ret) break; } if (is_add && !ret) kernfs_activate(root->kn); return ret; } static void cgroup_exit_cftypes(struct cftype *cfts) { struct cftype *cft; for (cft = cfts; cft->name[0] != '\0'; cft++) { /* free copy for custom atomic_write_len, see init_cftypes() */ if (cft->max_write_len && cft->max_write_len != PAGE_SIZE) kfree(cft->kf_ops); cft->kf_ops = NULL; cft->ss = NULL; } } static int cgroup_init_cftypes(struct cgroup_subsys *ss, struct cftype *cfts) { struct cftype *cft; for (cft = cfts; cft->name[0] != '\0'; cft++) { struct kernfs_ops *kf_ops; WARN_ON(cft->ss || cft->kf_ops); if (cft->seq_start) kf_ops = &cgroup_kf_ops; else kf_ops = &cgroup_kf_single_ops; /* * Ugh... if @cft wants a custom max_write_len, we need to * make a copy of kf_ops to set its atomic_write_len. */ if (cft->max_write_len && cft->max_write_len != PAGE_SIZE) { kf_ops = kmemdup(kf_ops, sizeof(*kf_ops), GFP_KERNEL); if (!kf_ops) { cgroup_exit_cftypes(cfts); return -ENOMEM; } kf_ops->atomic_write_len = cft->max_write_len; } cft->kf_ops = kf_ops; cft->ss = ss; } return 0; } static int cgroup_rm_cftypes_locked(struct cftype *cfts) { lockdep_assert_held(&cgroup_tree_mutex); if (!cfts || !cfts[0].ss) return -ENOENT; list_del(&cfts->node); cgroup_apply_cftypes(cfts, false); cgroup_exit_cftypes(cfts); return 0; } /** * cgroup_rm_cftypes - remove an array of cftypes from a subsystem * @cfts: zero-length name terminated array of cftypes * * Unregister @cfts. Files described by @cfts are removed from all * existing cgroups and all future cgroups won't have them either. This * function can be called anytime whether @cfts' subsys is attached or not. * * Returns 0 on successful unregistration, -ENOENT if @cfts is not * registered. */ int cgroup_rm_cftypes(struct cftype *cfts) { int ret; mutex_lock(&cgroup_tree_mutex); ret = cgroup_rm_cftypes_locked(cfts); mutex_unlock(&cgroup_tree_mutex); return ret; } /** * cgroup_add_cftypes - add an array of cftypes to a subsystem * @ss: target cgroup subsystem * @cfts: zero-length name terminated array of cftypes * * Register @cfts to @ss. Files described by @cfts are created for all * existing cgroups to which @ss is attached and all future cgroups will * have them too. This function can be called anytime whether @ss is * attached or not. * * Returns 0 on successful registration, -errno on failure. Note that this * function currently returns 0 as long as @cfts registration is successful * even if some file creation attempts on existing cgroups fail. */ int cgroup_add_cftypes(struct cgroup_subsys *ss, struct cftype *cfts) { int ret; if (!cfts || cfts[0].name[0] == '\0') return 0; ret = cgroup_init_cftypes(ss, cfts); if (ret) return ret; mutex_lock(&cgroup_tree_mutex); list_add_tail(&cfts->node, &ss->cfts); ret = cgroup_apply_cftypes(cfts, true); if (ret) cgroup_rm_cftypes_locked(cfts); mutex_unlock(&cgroup_tree_mutex); return ret; } /** * cgroup_task_count - count the number of tasks in a cgroup. * @cgrp: the cgroup in question * * Return the number of tasks in the cgroup. */ static int cgroup_task_count(const struct cgroup *cgrp) { int count = 0; struct cgrp_cset_link *link; down_read(&css_set_rwsem); list_for_each_entry(link, &cgrp->cset_links, cset_link) count += atomic_read(&link->cset->refcount); up_read(&css_set_rwsem); return count; } /** * css_next_child - find the next child of a given css * @pos_css: the current position (%NULL to initiate traversal) * @parent_css: css whose children to walk * * This function returns the next child of @parent_css and should be called * under either cgroup_mutex or RCU read lock. The only requirement is * that @parent_css and @pos_css are accessible. The next sibling is * guaranteed to be returned regardless of their states. */ struct cgroup_subsys_state * css_next_child(struct cgroup_subsys_state *pos_css, struct cgroup_subsys_state *parent_css) { struct cgroup *pos = pos_css ? pos_css->cgroup : NULL; struct cgroup *cgrp = parent_css->cgroup; struct cgroup *next; cgroup_assert_mutexes_or_rcu_locked(); /* * @pos could already have been removed. Once a cgroup is removed, * its ->sibling.next is no longer updated when its next sibling * changes. As CGRP_DEAD assertion is serialized and happens * before the cgroup is taken off the ->sibling list, if we see it * unasserted, it's guaranteed that the next sibling hasn't * finished its grace period even if it's already removed, and thus * safe to dereference from this RCU critical section. If * ->sibling.next is inaccessible, cgroup_is_dead() is guaranteed * to be visible as %true here. * * If @pos is dead, its next pointer can't be dereferenced; * however, as each cgroup is given a monotonically increasing * unique serial number and always appended to the sibling list, * the next one can be found by walking the parent's children until * we see a cgroup with higher serial number than @pos's. While * this path can be slower, it's taken only when either the current * cgroup is removed or iteration and removal race. */ if (!pos) { next = list_entry_rcu(cgrp->children.next, struct cgroup, sibling); } else if (likely(!cgroup_is_dead(pos))) { next = list_entry_rcu(pos->sibling.next, struct cgroup, sibling); } else { list_for_each_entry_rcu(next, &cgrp->children, sibling) if (next->serial_nr > pos->serial_nr) break; } if (&next->sibling == &cgrp->children) return NULL; return cgroup_css(next, parent_css->ss); } /** * css_next_descendant_pre - find the next descendant for pre-order walk * @pos: the current position (%NULL to initiate traversal) * @root: css whose descendants to walk * * To be used by css_for_each_descendant_pre(). Find the next descendant * to visit for pre-order traversal of @root's descendants. @root is * included in the iteration and the first node to be visited. * * While this function requires cgroup_mutex or RCU read locking, it * doesn't require the whole traversal to be contained in a single critical * section. This function will return the correct next descendant as long * as both @pos and @root are accessible and @pos is a descendant of @root. */ struct cgroup_subsys_state * css_next_descendant_pre(struct cgroup_subsys_state *pos, struct cgroup_subsys_state *root) { struct cgroup_subsys_state *next; cgroup_assert_mutexes_or_rcu_locked(); /* if first iteration, visit @root */ if (!pos) return root; /* visit the first child if exists */ next = css_next_child(NULL, pos); if (next) return next; /* no child, visit my or the closest ancestor's next sibling */ while (pos != root) { next = css_next_child(pos, css_parent(pos)); if (next) return next; pos = css_parent(pos); } return NULL; } /** * css_rightmost_descendant - return the rightmost descendant of a css * @pos: css of interest * * Return the rightmost descendant of @pos. If there's no descendant, @pos * is returned. This can be used during pre-order traversal to skip * subtree of @pos. * * While this function requires cgroup_mutex or RCU read locking, it * doesn't require the whole traversal to be contained in a single critical * section. This function will return the correct rightmost descendant as * long as @pos is accessible. */ struct cgroup_subsys_state * css_rightmost_descendant(struct cgroup_subsys_state *pos) { struct cgroup_subsys_state *last, *tmp; cgroup_assert_mutexes_or_rcu_locked(); do { last = pos; /* ->prev isn't RCU safe, walk ->next till the end */ pos = NULL; css_for_each_child(tmp, last) pos = tmp; } while (pos); return last; } static struct cgroup_subsys_state * css_leftmost_descendant(struct cgroup_subsys_state *pos) { struct cgroup_subsys_state *last; do { last = pos; pos = css_next_child(NULL, pos); } while (pos); return last; } /** * css_next_descendant_post - find the next descendant for post-order walk * @pos: the current position (%NULL to initiate traversal) * @root: css whose descendants to walk * * To be used by css_for_each_descendant_post(). Find the next descendant * to visit for post-order traversal of @root's descendants. @root is * included in the iteration and the last node to be visited. * * While this function requires cgroup_mutex or RCU read locking, it * doesn't require the whole traversal to be contained in a single critical * section. This function will return the correct next descendant as long * as both @pos and @cgroup are accessible and @pos is a descendant of * @cgroup. */ struct cgroup_subsys_state * css_next_descendant_post(struct cgroup_subsys_state *pos, struct cgroup_subsys_state *root) { struct cgroup_subsys_state *next; cgroup_assert_mutexes_or_rcu_locked(); /* if first iteration, visit leftmost descendant which may be @root */ if (!pos) return css_leftmost_descendant(root); /* if we visited @root, we're done */ if (pos == root) return NULL; /* if there's an unvisited sibling, visit its leftmost descendant */ next = css_next_child(pos, css_parent(pos)); if (next) return css_leftmost_descendant(next); /* no sibling left, visit parent */ return css_parent(pos); } /** * css_advance_task_iter - advance a task itererator to the next css_set * @it: the iterator to advance * * Advance @it to the next css_set to walk. */ static void css_advance_task_iter(struct css_task_iter *it) { struct list_head *l = it->cset_link; struct cgrp_cset_link *link; struct css_set *cset; /* Advance to the next non-empty css_set */ do { l = l->next; if (l == &it->origin_css->cgroup->cset_links) { it->cset_link = NULL; return; } link = list_entry(l, struct cgrp_cset_link, cset_link); cset = link->cset; } while (list_empty(&cset->tasks) && list_empty(&cset->mg_tasks)); it->cset_link = l; if (!list_empty(&cset->tasks)) it->task = cset->tasks.next; else it->task = cset->mg_tasks.next; } /** * css_task_iter_start - initiate task iteration * @css: the css to walk tasks of * @it: the task iterator to use * * Initiate iteration through the tasks of @css. The caller can call * css_task_iter_next() to walk through the tasks until the function * returns NULL. On completion of iteration, css_task_iter_end() must be * called. * * Note that this function acquires a lock which is released when the * iteration finishes. The caller can't sleep while iteration is in * progress. */ void css_task_iter_start(struct cgroup_subsys_state *css, struct css_task_iter *it) __acquires(css_set_rwsem) { /* no one should try to iterate before mounting cgroups */ WARN_ON_ONCE(!use_task_css_set_links); down_read(&css_set_rwsem); it->origin_css = css; it->cset_link = &css->cgroup->cset_links; css_advance_task_iter(it); } /** * css_task_iter_next - return the next task for the iterator * @it: the task iterator being iterated * * The "next" function for task iteration. @it should have been * initialized via css_task_iter_start(). Returns NULL when the iteration * reaches the end. */ struct task_struct *css_task_iter_next(struct css_task_iter *it) { struct task_struct *res; struct list_head *l = it->task; struct cgrp_cset_link *link = list_entry(it->cset_link, struct cgrp_cset_link, cset_link); /* If the iterator cg is NULL, we have no tasks */ if (!it->cset_link) return NULL; res = list_entry(l, struct task_struct, cg_list); /* * Advance iterator to find next entry. cset->tasks is consumed * first and then ->mg_tasks. After ->mg_tasks, we move onto the * next cset. */ l = l->next; if (l == &link->cset->tasks) l = link->cset->mg_tasks.next; if (l == &link->cset->mg_tasks) css_advance_task_iter(it); else it->task = l; return res; } /** * css_task_iter_end - finish task iteration * @it: the task iterator to finish * * Finish task iteration started by css_task_iter_start(). */ void css_task_iter_end(struct css_task_iter *it) __releases(css_set_rwsem) { up_read(&css_set_rwsem); } /** * cgroup_trasnsfer_tasks - move tasks from one cgroup to another * @to: cgroup to which the tasks will be moved * @from: cgroup in which the tasks currently reside * * Locking rules between cgroup_post_fork() and the migration path * guarantee that, if a task is forking while being migrated, the new child * is guaranteed to be either visible in the source cgroup after the * parent's migration is complete or put into the target cgroup. No task * can slip out of migration through forking. */ int cgroup_transfer_tasks(struct cgroup *to, struct cgroup *from) { LIST_HEAD(preloaded_csets); struct cgrp_cset_link *link; struct css_task_iter it; struct task_struct *task; int ret; mutex_lock(&cgroup_mutex); /* all tasks in @from are being moved, all csets are source */ down_read(&css_set_rwsem); list_for_each_entry(link, &from->cset_links, cset_link) cgroup_migrate_add_src(link->cset, to, &preloaded_csets); up_read(&css_set_rwsem); ret = cgroup_migrate_prepare_dst(to, &preloaded_csets); if (ret) goto out_err; /* * Migrate tasks one-by-one until @form is empty. This fails iff * ->can_attach() fails. */ do { css_task_iter_start(&from->dummy_css, &it); task = css_task_iter_next(&it); if (task) get_task_struct(task); css_task_iter_end(&it); if (task) { ret = cgroup_migrate(to, task, false); put_task_struct(task); } } while (task && !ret); out_err: cgroup_migrate_finish(&preloaded_csets); mutex_unlock(&cgroup_mutex); return ret; } /* * Stuff for reading the 'tasks'/'procs' files. * * Reading this file can return large amounts of data if a cgroup has * *lots* of attached tasks. So it may need several calls to read(), * but we cannot guarantee that the information we produce is correct * unless we produce it entirely atomically. * */ /* which pidlist file are we talking about? */ enum cgroup_filetype { CGROUP_FILE_PROCS, CGROUP_FILE_TASKS, }; /* * A pidlist is a list of pids that virtually represents the contents of one * of the cgroup files ("procs" or "tasks"). We keep a list of such pidlists, * a pair (one each for procs, tasks) for each pid namespace that's relevant * to the cgroup. */ struct cgroup_pidlist { /* * used to find which pidlist is wanted. doesn't change as long as * this particular list stays in the list. */ struct { enum cgroup_filetype type; struct pid_namespace *ns; } key; /* array of xids */ pid_t *list; /* how many elements the above list has */ int length; /* each of these stored in a list by its cgroup */ struct list_head links; /* pointer to the cgroup we belong to, for list removal purposes */ struct cgroup *owner; /* for delayed destruction */ struct delayed_work destroy_dwork; }; /* * The following two functions "fix" the issue where there are more pids * than kmalloc will give memory for; in such cases, we use vmalloc/vfree. * TODO: replace with a kernel-wide solution to this problem */ #define PIDLIST_TOO_LARGE(c) ((c) * sizeof(pid_t) > (PAGE_SIZE * 2)) static void *pidlist_allocate(int count) { if (PIDLIST_TOO_LARGE(count)) return vmalloc(count * sizeof(pid_t)); else return kmalloc(count * sizeof(pid_t), GFP_KERNEL); } static void pidlist_free(void *p) { if (is_vmalloc_addr(p)) vfree(p); else kfree(p); } /* * Used to destroy all pidlists lingering waiting for destroy timer. None * should be left afterwards. */ static void cgroup_pidlist_destroy_all(struct cgroup *cgrp) { struct cgroup_pidlist *l, *tmp_l; mutex_lock(&cgrp->pidlist_mutex); list_for_each_entry_safe(l, tmp_l, &cgrp->pidlists, links) mod_delayed_work(cgroup_pidlist_destroy_wq, &l->destroy_dwork, 0); mutex_unlock(&cgrp->pidlist_mutex); flush_workqueue(cgroup_pidlist_destroy_wq); BUG_ON(!list_empty(&cgrp->pidlists)); } static void cgroup_pidlist_destroy_work_fn(struct work_struct *work) { struct delayed_work *dwork = to_delayed_work(work); struct cgroup_pidlist *l = container_of(dwork, struct cgroup_pidlist, destroy_dwork); struct cgroup_pidlist *tofree = NULL; mutex_lock(&l->owner->pidlist_mutex); /* * Destroy iff we didn't get queued again. The state won't change * as destroy_dwork can only be queued while locked. */ if (!delayed_work_pending(dwork)) { list_del(&l->links); pidlist_free(l->list); put_pid_ns(l->key.ns); tofree = l; } mutex_unlock(&l->owner->pidlist_mutex); kfree(tofree); } /* * pidlist_uniq - given a kmalloc()ed list, strip out all duplicate entries * Returns the number of unique elements. */ static int pidlist_uniq(pid_t *list, int length) { int src, dest = 1; /* * we presume the 0th element is unique, so i starts at 1. trivial * edge cases first; no work needs to be done for either */ if (length == 0 || length == 1) return length; /* src and dest walk down the list; dest counts unique elements */ for (src = 1; src < length; src++) { /* find next unique element */ while (list[src] == list[src-1]) { src++; if (src == length) goto after; } /* dest always points to where the next unique element goes */ list[dest] = list[src]; dest++; } after: return dest; } /* * The two pid files - task and cgroup.procs - guaranteed that the result * is sorted, which forced this whole pidlist fiasco. As pid order is * different per namespace, each namespace needs differently sorted list, * making it impossible to use, for example, single rbtree of member tasks * sorted by task pointer. As pidlists can be fairly large, allocating one * per open file is dangerous, so cgroup had to implement shared pool of * pidlists keyed by cgroup and namespace. * * All this extra complexity was caused by the original implementation * committing to an entirely unnecessary property. In the long term, we * want to do away with it. Explicitly scramble sort order if * sane_behavior so that no such expectation exists in the new interface. * * Scrambling is done by swapping every two consecutive bits, which is * non-identity one-to-one mapping which disturbs sort order sufficiently. */ static pid_t pid_fry(pid_t pid) { unsigned a = pid & 0x55555555; unsigned b = pid & 0xAAAAAAAA; return (a << 1) | (b >> 1); } static pid_t cgroup_pid_fry(struct cgroup *cgrp, pid_t pid) { if (cgroup_sane_behavior(cgrp)) return pid_fry(pid); else return pid; } static int cmppid(const void *a, const void *b) { return *(pid_t *)a - *(pid_t *)b; } static int fried_cmppid(const void *a, const void *b) { return pid_fry(*(pid_t *)a) - pid_fry(*(pid_t *)b); } static struct cgroup_pidlist *cgroup_pidlist_find(struct cgroup *cgrp, enum cgroup_filetype type) { struct cgroup_pidlist *l; /* don't need task_nsproxy() if we're looking at ourself */ struct pid_namespace *ns = task_active_pid_ns(current); lockdep_assert_held(&cgrp->pidlist_mutex); list_for_each_entry(l, &cgrp->pidlists, links) if (l->key.type == type && l->key.ns == ns) return l; return NULL; } /* * find the appropriate pidlist for our purpose (given procs vs tasks) * returns with the lock on that pidlist already held, and takes care * of the use count, or returns NULL with no locks held if we're out of * memory. */ static struct cgroup_pidlist *cgroup_pidlist_find_create(struct cgroup *cgrp, enum cgroup_filetype type) { struct cgroup_pidlist *l; lockdep_assert_held(&cgrp->pidlist_mutex); l = cgroup_pidlist_find(cgrp, type); if (l) return l; /* entry not found; create a new one */ l = kzalloc(sizeof(struct cgroup_pidlist), GFP_KERNEL); if (!l) return l; INIT_DELAYED_WORK(&l->destroy_dwork, cgroup_pidlist_destroy_work_fn); l->key.type = type; /* don't need task_nsproxy() if we're looking at ourself */ l->key.ns = get_pid_ns(task_active_pid_ns(current)); l->owner = cgrp; list_add(&l->links, &cgrp->pidlists); return l; } /* * Load a cgroup's pidarray with either procs' tgids or tasks' pids */ static int pidlist_array_load(struct cgroup *cgrp, enum cgroup_filetype type, struct cgroup_pidlist **lp) { pid_t *array; int length; int pid, n = 0; /* used for populating the array */ struct css_task_iter it; struct task_struct *tsk; struct cgroup_pidlist *l; lockdep_assert_held(&cgrp->pidlist_mutex); /* * If cgroup gets more users after we read count, we won't have * enough space - tough. This race is indistinguishable to the * caller from the case that the additional cgroup users didn't * show up until sometime later on. */ length = cgroup_task_count(cgrp); array = pidlist_allocate(length); if (!array) return -ENOMEM; /* now, populate the array */ css_task_iter_start(&cgrp->dummy_css, &it); while ((tsk = css_task_iter_next(&it))) { if (unlikely(n == length)) break; /* get tgid or pid for procs or tasks file respectively */ if (type == CGROUP_FILE_PROCS) pid = task_tgid_vnr(tsk); else pid = task_pid_vnr(tsk); if (pid > 0) /* make sure to only use valid results */ array[n++] = pid; } css_task_iter_end(&it); length = n; /* now sort & (if procs) strip out duplicates */ if (cgroup_sane_behavior(cgrp)) sort(array, length, sizeof(pid_t), fried_cmppid, NULL); else sort(array, length, sizeof(pid_t), cmppid, NULL); if (type == CGROUP_FILE_PROCS) length = pidlist_uniq(array, length); l = cgroup_pidlist_find_create(cgrp, type); if (!l) { mutex_unlock(&cgrp->pidlist_mutex); pidlist_free(array); return -ENOMEM; } /* store array, freeing old if necessary */ pidlist_free(l->list); l->list = array; l->length = length; *lp = l; return 0; } /** * cgroupstats_build - build and fill cgroupstats * @stats: cgroupstats to fill information into * @dentry: A dentry entry belonging to the cgroup for which stats have * been requested. * * Build and fill cgroupstats so that taskstats can export it to user * space. */ int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry) { struct kernfs_node *kn = kernfs_node_from_dentry(dentry); struct cgroup *cgrp; struct css_task_iter it; struct task_struct *tsk; /* it should be kernfs_node belonging to cgroupfs and is a directory */ if (dentry->d_sb->s_type != &cgroup_fs_type || !kn || kernfs_type(kn) != KERNFS_DIR) return -EINVAL; mutex_lock(&cgroup_mutex); /* * We aren't being called from kernfs and there's no guarantee on * @kn->priv's validity. For this and css_tryget_from_dir(), * @kn->priv is RCU safe. Let's do the RCU dancing. */ rcu_read_lock(); cgrp = rcu_dereference(kn->priv); if (!cgrp || cgroup_is_dead(cgrp)) { rcu_read_unlock(); mutex_unlock(&cgroup_mutex); return -ENOENT; } rcu_read_unlock(); css_task_iter_start(&cgrp->dummy_css, &it); while ((tsk = css_task_iter_next(&it))) { switch (tsk->state) { case TASK_RUNNING: stats->nr_running++; break; case TASK_INTERRUPTIBLE: stats->nr_sleeping++; break; case TASK_UNINTERRUPTIBLE: stats->nr_uninterruptible++; break; case TASK_STOPPED: stats->nr_stopped++; break; default: if (delayacct_is_task_waiting_on_io(tsk)) stats->nr_io_wait++; break; } } css_task_iter_end(&it); mutex_unlock(&cgroup_mutex); return 0; } /* * seq_file methods for the tasks/procs files. The seq_file position is the * next pid to display; the seq_file iterator is a pointer to the pid * in the cgroup->l->list array. */ static void *cgroup_pidlist_start(struct seq_file *s, loff_t *pos) { /* * Initially we receive a position value that corresponds to * one more than the last pid shown (or 0 on the first call or * after a seek to the start). Use a binary-search to find the * next pid to display, if any */ struct kernfs_open_file *of = s->private; struct cgroup *cgrp = seq_css(s)->cgroup; struct cgroup_pidlist *l; enum cgroup_filetype type = seq_cft(s)->private; int index = 0, pid = *pos; int *iter, ret; mutex_lock(&cgrp->pidlist_mutex); /* * !NULL @of->priv indicates that this isn't the first start() * after open. If the matching pidlist is around, we can use that. * Look for it. Note that @of->priv can't be used directly. It * could already have been destroyed. */ if (of->priv) of->priv = cgroup_pidlist_find(cgrp, type); /* * Either this is the first start() after open or the matching * pidlist has been destroyed inbetween. Create a new one. */ if (!of->priv) { ret = pidlist_array_load(cgrp, type, (struct cgroup_pidlist **)&of->priv); if (ret) return ERR_PTR(ret); } l = of->priv; if (pid) { int end = l->length; while (index < end) { int mid = (index + end) / 2; if (cgroup_pid_fry(cgrp, l->list[mid]) == pid) { index = mid; break; } else if (cgroup_pid_fry(cgrp, l->list[mid]) <= pid) index = mid + 1; else end = mid; } } /* If we're off the end of the array, we're done */ if (index >= l->length) return NULL; /* Update the abstract position to be the actual pid that we found */ iter = l->list + index; *pos = cgroup_pid_fry(cgrp, *iter); return iter; } static void cgroup_pidlist_stop(struct seq_file *s, void *v) { struct kernfs_open_file *of = s->private; struct cgroup_pidlist *l = of->priv; if (l) mod_delayed_work(cgroup_pidlist_destroy_wq, &l->destroy_dwork, CGROUP_PIDLIST_DESTROY_DELAY); mutex_unlock(&seq_css(s)->cgroup->pidlist_mutex); } static void *cgroup_pidlist_next(struct seq_file *s, void *v, loff_t *pos) { struct kernfs_open_file *of = s->private; struct cgroup_pidlist *l = of->priv; pid_t *p = v; pid_t *end = l->list + l->length; /* * Advance to the next pid in the array. If this goes off the * end, we're done */ p++; if (p >= end) { return NULL; } else { *pos = cgroup_pid_fry(seq_css(s)->cgroup, *p); return p; } } static int cgroup_pidlist_show(struct seq_file *s, void *v) { return seq_printf(s, "%d\n", *(int *)v); } /* * seq_operations functions for iterating on pidlists through seq_file - * independent of whether it's tasks or procs */ static const struct seq_operations cgroup_pidlist_seq_operations = { .start = cgroup_pidlist_start, .stop = cgroup_pidlist_stop, .next = cgroup_pidlist_next, .show = cgroup_pidlist_show, }; static u64 cgroup_read_notify_on_release(struct cgroup_subsys_state *css, struct cftype *cft) { return notify_on_release(css->cgroup); } static int cgroup_write_notify_on_release(struct cgroup_subsys_state *css, struct cftype *cft, u64 val) { clear_bit(CGRP_RELEASABLE, &css->cgroup->flags); if (val) set_bit(CGRP_NOTIFY_ON_RELEASE, &css->cgroup->flags); else clear_bit(CGRP_NOTIFY_ON_RELEASE, &css->cgroup->flags); return 0; } static u64 cgroup_clone_children_read(struct cgroup_subsys_state *css, struct cftype *cft) { return test_bit(CGRP_CPUSET_CLONE_CHILDREN, &css->cgroup->flags); } static int cgroup_clone_children_write(struct cgroup_subsys_state *css, struct cftype *cft, u64 val) { if (val) set_bit(CGRP_CPUSET_CLONE_CHILDREN, &css->cgroup->flags); else clear_bit(CGRP_CPUSET_CLONE_CHILDREN, &css->cgroup->flags); return 0; } static struct cftype cgroup_base_files[] = { { .name = "cgroup.procs", .seq_start = cgroup_pidlist_start, .seq_next = cgroup_pidlist_next, .seq_stop = cgroup_pidlist_stop, .seq_show = cgroup_pidlist_show, .private = CGROUP_FILE_PROCS, .write_u64 = cgroup_procs_write, .mode = S_IRUGO | S_IWUSR, }, { .name = "cgroup.clone_children", .flags = CFTYPE_INSANE, .read_u64 = cgroup_clone_children_read, .write_u64 = cgroup_clone_children_write, }, { .name = "cgroup.sane_behavior", .flags = CFTYPE_ONLY_ON_ROOT, .seq_show = cgroup_sane_behavior_show, }, /* * Historical crazy stuff. These don't have "cgroup." prefix and * don't exist if sane_behavior. If you're depending on these, be * prepared to be burned. */ { .name = "tasks", .flags = CFTYPE_INSANE, /* use "procs" instead */ .seq_start = cgroup_pidlist_start, .seq_next = cgroup_pidlist_next, .seq_stop = cgroup_pidlist_stop, .seq_show = cgroup_pidlist_show, .private = CGROUP_FILE_TASKS, .write_u64 = cgroup_tasks_write, .mode = S_IRUGO | S_IWUSR, }, { .name = "notify_on_release", .flags = CFTYPE_INSANE, .read_u64 = cgroup_read_notify_on_release, .write_u64 = cgroup_write_notify_on_release, }, { .name = "release_agent", .flags = CFTYPE_INSANE | CFTYPE_ONLY_ON_ROOT, .seq_show = cgroup_release_agent_show, .write_string = cgroup_release_agent_write, .max_write_len = PATH_MAX - 1, }, { } /* terminate */ }; /** * cgroup_populate_dir - create subsys files in a cgroup directory * @cgrp: target cgroup * @subsys_mask: mask of the subsystem ids whose files should be added * * On failure, no file is added. */ static int cgroup_populate_dir(struct cgroup *cgrp, unsigned long subsys_mask) { struct cgroup_subsys *ss; int i, ret = 0; /* process cftsets of each subsystem */ for_each_subsys(ss, i) { struct cftype *cfts; if (!test_bit(i, &subsys_mask)) continue; list_for_each_entry(cfts, &ss->cfts, node) { ret = cgroup_addrm_files(cgrp, cfts, true); if (ret < 0) goto err; } } return 0; err: cgroup_clear_dir(cgrp, subsys_mask); return ret; } /* * css destruction is four-stage process. * * 1. Destruction starts. Killing of the percpu_ref is initiated. * Implemented in kill_css(). * * 2. When the percpu_ref is confirmed to be visible as killed on all CPUs * and thus css_tryget() is guaranteed to fail, the css can be offlined * by invoking offline_css(). After offlining, the base ref is put. * Implemented in css_killed_work_fn(). * * 3. When the percpu_ref reaches zero, the only possible remaining * accessors are inside RCU read sections. css_release() schedules the * RCU callback. * * 4. After the grace period, the css can be freed. Implemented in * css_free_work_fn(). * * It is actually hairier because both step 2 and 4 require process context * and thus involve punting to css->destroy_work adding two additional * steps to the already complex sequence. */ static void css_free_work_fn(struct work_struct *work) { struct cgroup_subsys_state *css = container_of(work, struct cgroup_subsys_state, destroy_work); struct cgroup *cgrp = css->cgroup; if (css->parent) css_put(css->parent); css->ss->css_free(css); cgroup_put(cgrp); } static void css_free_rcu_fn(struct rcu_head *rcu_head) { struct cgroup_subsys_state *css = container_of(rcu_head, struct cgroup_subsys_state, rcu_head); INIT_WORK(&css->destroy_work, css_free_work_fn); queue_work(cgroup_destroy_wq, &css->destroy_work); } static void css_release(struct percpu_ref *ref) { struct cgroup_subsys_state *css = container_of(ref, struct cgroup_subsys_state, refcnt); rcu_assign_pointer(css->cgroup->subsys[css->ss->id], NULL); call_rcu(&css->rcu_head, css_free_rcu_fn); } static void init_css(struct cgroup_subsys_state *css, struct cgroup_subsys *ss, struct cgroup *cgrp) { css->cgroup = cgrp; css->ss = ss; css->flags = 0; if (cgrp->parent) css->parent = cgroup_css(cgrp->parent, ss); else css->flags |= CSS_ROOT; BUG_ON(cgroup_css(cgrp, ss)); } /* invoke ->css_online() on a new CSS and mark it online if successful */ static int online_css(struct cgroup_subsys_state *css) { struct cgroup_subsys *ss = css->ss; int ret = 0; lockdep_assert_held(&cgroup_tree_mutex); lockdep_assert_held(&cgroup_mutex); if (ss->css_online) ret = ss->css_online(css); if (!ret) { css->flags |= CSS_ONLINE; css->cgroup->nr_css++; rcu_assign_pointer(css->cgroup->subsys[ss->id], css); } return ret; } /* if the CSS is online, invoke ->css_offline() on it and mark it offline */ static void offline_css(struct cgroup_subsys_state *css) { struct cgroup_subsys *ss = css->ss; lockdep_assert_held(&cgroup_tree_mutex); lockdep_assert_held(&cgroup_mutex); if (!(css->flags & CSS_ONLINE)) return; if (ss->css_offline) ss->css_offline(css); css->flags &= ~CSS_ONLINE; css->cgroup->nr_css--; RCU_INIT_POINTER(css->cgroup->subsys[ss->id], css); } /** * create_css - create a cgroup_subsys_state * @cgrp: the cgroup new css will be associated with * @ss: the subsys of new css * * Create a new css associated with @cgrp - @ss pair. On success, the new * css is online and installed in @cgrp with all interface files created. * Returns 0 on success, -errno on failure. */ static int create_css(struct cgroup *cgrp, struct cgroup_subsys *ss) { struct cgroup *parent = cgrp->parent; struct cgroup_subsys_state *css; int err; lockdep_assert_held(&cgroup_mutex); css = ss->css_alloc(cgroup_css(parent, ss)); if (IS_ERR(css)) return PTR_ERR(css); err = percpu_ref_init(&css->refcnt, css_release); if (err) goto err_free; init_css(css, ss, cgrp); err = cgroup_populate_dir(cgrp, 1 << ss->id); if (err) goto err_free; err = online_css(css); if (err) goto err_free; cgroup_get(cgrp); css_get(css->parent); cgrp->subsys_mask |= 1 << ss->id; if (ss->broken_hierarchy && !ss->warned_broken_hierarchy && parent->parent) { pr_warning("cgroup: %s (%d) created nested cgroup for controller \"%s\" which has incomplete hierarchy support. Nested cgroups may change behavior in the future.\n", current->comm, current->pid, ss->name); if (!strcmp(ss->name, "memory")) pr_warning("cgroup: \"memory\" requires setting use_hierarchy to 1 on the root.\n"); ss->warned_broken_hierarchy = true; } return 0; err_free: percpu_ref_cancel_init(&css->refcnt); ss->css_free(css); return err; } /** * cgroup_create - create a cgroup * @parent: cgroup that will be parent of the new cgroup * @name: name of the new cgroup * @mode: mode to set on new cgroup */ static long cgroup_create(struct cgroup *parent, const char *name, umode_t mode) { struct cgroup *cgrp; struct cgroup_root *root = parent->root; int ssid, err; struct cgroup_subsys *ss; struct kernfs_node *kn; /* * XXX: The default hierarchy isn't fully implemented yet. Block * !root cgroup creation on it for now. */ if (root == &cgrp_dfl_root) return -EINVAL; /* allocate the cgroup and its ID, 0 is reserved for the root */ cgrp = kzalloc(sizeof(*cgrp), GFP_KERNEL); if (!cgrp) return -ENOMEM; mutex_lock(&cgroup_tree_mutex); /* * Only live parents can have children. Note that the liveliness * check isn't strictly necessary because cgroup_mkdir() and * cgroup_rmdir() are fully synchronized by i_mutex; however, do it * anyway so that locking is contained inside cgroup proper and we * don't get nasty surprises if we ever grow another caller. */ if (!cgroup_lock_live_group(parent)) { err = -ENODEV; goto err_unlock_tree; } /* * Temporarily set the pointer to NULL, so idr_find() won't return * a half-baked cgroup. */ cgrp->id = idr_alloc(&root->cgroup_idr, NULL, 1, 0, GFP_KERNEL); if (cgrp->id < 0) { err = -ENOMEM; goto err_unlock; } init_cgroup_housekeeping(cgrp); cgrp->parent = parent; cgrp->dummy_css.parent = &parent->dummy_css; cgrp->root = parent->root; if (notify_on_release(parent)) set_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags); if (test_bit(CGRP_CPUSET_CLONE_CHILDREN, &parent->flags)) set_bit(CGRP_CPUSET_CLONE_CHILDREN, &cgrp->flags); /* create the directory */ kn = kernfs_create_dir(parent->kn, name, mode, cgrp); if (IS_ERR(kn)) { err = PTR_ERR(kn); goto err_free_id; } cgrp->kn = kn; /* * This extra ref will be put in cgroup_free_fn() and guarantees * that @cgrp->kn is always accessible. */ kernfs_get(kn); cgrp->serial_nr = cgroup_serial_nr_next++; /* allocation complete, commit to creation */ list_add_tail_rcu(&cgrp->sibling, &cgrp->parent->children); atomic_inc(&root->nr_cgrps); cgroup_get(parent); /* * @cgrp is now fully operational. If something fails after this * point, it'll be released via the normal destruction path. */ idr_replace(&root->cgroup_idr, cgrp, cgrp->id); err = cgroup_addrm_files(cgrp, cgroup_base_files, true); if (err) goto err_destroy; /* let's create and online css's */ for_each_subsys(ss, ssid) { if (root->cgrp.subsys_mask & (1 << ssid)) { err = create_css(cgrp, ss); if (err) goto err_destroy; } } kernfs_activate(kn); mutex_unlock(&cgroup_mutex); mutex_unlock(&cgroup_tree_mutex); return 0; err_free_id: idr_remove(&root->cgroup_idr, cgrp->id); err_unlock: mutex_unlock(&cgroup_mutex); err_unlock_tree: mutex_unlock(&cgroup_tree_mutex); kfree(cgrp); return err; err_destroy: cgroup_destroy_locked(cgrp); mutex_unlock(&cgroup_mutex); mutex_unlock(&cgroup_tree_mutex); return err; } static int cgroup_mkdir(struct kernfs_node *parent_kn, const char *name, umode_t mode) { struct cgroup *parent = parent_kn->priv; return cgroup_create(parent, name, mode); } /* * This is called when the refcnt of a css is confirmed to be killed. * css_tryget() is now guaranteed to fail. */ static void css_killed_work_fn(struct work_struct *work) { struct cgroup_subsys_state *css = container_of(work, struct cgroup_subsys_state, destroy_work); struct cgroup *cgrp = css->cgroup; mutex_lock(&cgroup_tree_mutex); mutex_lock(&cgroup_mutex); /* * css_tryget() is guaranteed to fail now. Tell subsystems to * initate destruction. */ offline_css(css); /* * If @cgrp is marked dead, it's waiting for refs of all css's to * be disabled before proceeding to the second phase of cgroup * destruction. If we are the last one, kick it off. */ if (!cgrp->nr_css && cgroup_is_dead(cgrp)) cgroup_destroy_css_killed(cgrp); mutex_unlock(&cgroup_mutex); mutex_unlock(&cgroup_tree_mutex); /* * Put the css refs from kill_css(). Each css holds an extra * reference to the cgroup's dentry and cgroup removal proceeds * regardless of css refs. On the last put of each css, whenever * that may be, the extra dentry ref is put so that dentry * destruction happens only after all css's are released. */ css_put(css); } /* css kill confirmation processing requires process context, bounce */ static void css_killed_ref_fn(struct percpu_ref *ref) { struct cgroup_subsys_state *css = container_of(ref, struct cgroup_subsys_state, refcnt); INIT_WORK(&css->destroy_work, css_killed_work_fn); queue_work(cgroup_destroy_wq, &css->destroy_work); } static void __kill_css(struct cgroup_subsys_state *css) { lockdep_assert_held(&cgroup_tree_mutex); /* * This must happen before css is disassociated with its cgroup. * See seq_css() for details. */ cgroup_clear_dir(css->cgroup, 1 << css->ss->id); /* * Killing would put the base ref, but we need to keep it alive * until after ->css_offline(). */ css_get(css); /* * cgroup core guarantees that, by the time ->css_offline() is * invoked, no new css reference will be given out via * css_tryget(). We can't simply call percpu_ref_kill() and * proceed to offlining css's because percpu_ref_kill() doesn't * guarantee that the ref is seen as killed on all CPUs on return. * * Use percpu_ref_kill_and_confirm() to get notifications as each * css is confirmed to be seen as killed on all CPUs. */ percpu_ref_kill_and_confirm(&css->refcnt, css_killed_ref_fn); } /** * kill_css - destroy a css * @css: css to destroy * * This function initiates destruction of @css by removing cgroup interface * files and putting its base reference. ->css_offline() will be invoked * asynchronously once css_tryget() is guaranteed to fail and when the * reference count reaches zero, @css will be released. */ static void kill_css(struct cgroup_subsys_state *css) { struct cgroup *cgrp = css->cgroup; lockdep_assert_held(&cgroup_tree_mutex); /* if already killed, noop */ if (cgrp->subsys_mask & (1 << css->ss->id)) { cgrp->subsys_mask &= ~(1 << css->ss->id); __kill_css(css); } } /** * cgroup_destroy_locked - the first stage of cgroup destruction * @cgrp: cgroup to be destroyed * * css's make use of percpu refcnts whose killing latency shouldn't be * exposed to userland and are RCU protected. Also, cgroup core needs to * guarantee that css_tryget() won't succeed by the time ->css_offline() is * invoked. To satisfy all the requirements, destruction is implemented in * the following two steps. * * s1. Verify @cgrp can be destroyed and mark it dying. Remove all * userland visible parts and start killing the percpu refcnts of * css's. Set up so that the next stage will be kicked off once all * the percpu refcnts are confirmed to be killed. * * s2. Invoke ->css_offline(), mark the cgroup dead and proceed with the * rest of destruction. Once all cgroup references are gone, the * cgroup is RCU-freed. * * This function implements s1. After this step, @cgrp is gone as far as * the userland is concerned and a new cgroup with the same name may be * created. As cgroup doesn't care about the names internally, this * doesn't cause any problem. */ static int cgroup_destroy_locked(struct cgroup *cgrp) __releases(&cgroup_mutex) __acquires(&cgroup_mutex) { struct cgroup *child; struct cgroup_subsys_state *css; bool empty; int ssid; lockdep_assert_held(&cgroup_tree_mutex); lockdep_assert_held(&cgroup_mutex); /* * css_set_rwsem synchronizes access to ->cset_links and prevents * @cgrp from being removed while put_css_set() is in progress. */ down_read(&css_set_rwsem); empty = list_empty(&cgrp->cset_links); up_read(&css_set_rwsem); if (!empty) return -EBUSY; /* * Make sure there's no live children. We can't test ->children * emptiness as dead children linger on it while being destroyed; * otherwise, "rmdir parent/child parent" may fail with -EBUSY. */ empty = true; rcu_read_lock(); list_for_each_entry_rcu(child, &cgrp->children, sibling) { empty = cgroup_is_dead(child); if (!empty) break; } rcu_read_unlock(); if (!empty) return -EBUSY; /* * Mark @cgrp dead. This prevents further task migration and child * creation by disabling cgroup_lock_live_group(). Note that * CGRP_DEAD assertion is depended upon by css_next_child() to * resume iteration after dropping RCU read lock. See * css_next_child() for details. */ set_bit(CGRP_DEAD, &cgrp->flags); /* * Initiate massacre of all css's. cgroup_destroy_css_killed() * will be invoked to perform the rest of destruction once the * percpu refs of all css's are confirmed to be killed. This * involves removing the subsystem's files, drop cgroup_mutex. */ mutex_unlock(&cgroup_mutex); for_each_css(css, ssid, cgrp) kill_css(css); mutex_lock(&cgroup_mutex); /* CGRP_DEAD is set, remove from ->release_list for the last time */ raw_spin_lock(&release_list_lock); if (!list_empty(&cgrp->release_list)) list_del_init(&cgrp->release_list); raw_spin_unlock(&release_list_lock); /* * If @cgrp has css's attached, the second stage of cgroup * destruction is kicked off from css_killed_work_fn() after the * refs of all attached css's are killed. If @cgrp doesn't have * any css, we kick it off here. */ if (!cgrp->nr_css) cgroup_destroy_css_killed(cgrp); /* remove @cgrp directory along with the base files */ mutex_unlock(&cgroup_mutex); /* * There are two control paths which try to determine cgroup from * dentry without going through kernfs - cgroupstats_build() and * css_tryget_from_dir(). Those are supported by RCU protecting * clearing of cgrp->kn->priv backpointer, which should happen * after all files under it have been removed. */ kernfs_remove(cgrp->kn); /* @cgrp has an extra ref on its kn */ RCU_INIT_POINTER(*(void __rcu __force **)&cgrp->kn->priv, NULL); mutex_lock(&cgroup_mutex); return 0; }; /** * cgroup_destroy_css_killed - the second step of cgroup destruction * @work: cgroup->destroy_free_work * * This function is invoked from a work item for a cgroup which is being * destroyed after all css's are offlined and performs the rest of * destruction. This is the second step of destruction described in the * comment above cgroup_destroy_locked(). */ static void cgroup_destroy_css_killed(struct cgroup *cgrp) { struct cgroup *parent = cgrp->parent; lockdep_assert_held(&cgroup_tree_mutex); lockdep_assert_held(&cgroup_mutex); /* delete this cgroup from parent->children */ list_del_rcu(&cgrp->sibling); cgroup_put(cgrp); set_bit(CGRP_RELEASABLE, &parent->flags); check_for_release(parent); } static int cgroup_rmdir(struct kernfs_node *kn) { struct cgroup *cgrp = kn->priv; int ret = 0; /* * This is self-destruction but @kn can't be removed while this * callback is in progress. Let's break active protection. Once * the protection is broken, @cgrp can be destroyed at any point. * Pin it so that it stays accessible. */ cgroup_get(cgrp); kernfs_break_active_protection(kn); mutex_lock(&cgroup_tree_mutex); mutex_lock(&cgroup_mutex); /* * @cgrp might already have been destroyed while we're trying to * grab the mutexes. */ if (!cgroup_is_dead(cgrp)) ret = cgroup_destroy_locked(cgrp); mutex_unlock(&cgroup_mutex); mutex_unlock(&cgroup_tree_mutex); kernfs_unbreak_active_protection(kn); cgroup_put(cgrp); return ret; } static struct kernfs_syscall_ops cgroup_kf_syscall_ops = { .remount_fs = cgroup_remount, .show_options = cgroup_show_options, .mkdir = cgroup_mkdir, .rmdir = cgroup_rmdir, .rename = cgroup_rename, }; static void __init cgroup_init_subsys(struct cgroup_subsys *ss) { struct cgroup_subsys_state *css; printk(KERN_INFO "Initializing cgroup subsys %s\n", ss->name); mutex_lock(&cgroup_tree_mutex); mutex_lock(&cgroup_mutex); INIT_LIST_HEAD(&ss->cfts); /* Create the root cgroup state for this subsystem */ ss->root = &cgrp_dfl_root; css = ss->css_alloc(cgroup_css(&cgrp_dfl_root.cgrp, ss)); /* We don't handle early failures gracefully */ BUG_ON(IS_ERR(css)); init_css(css, ss, &cgrp_dfl_root.cgrp); /* Update the init_css_set to contain a subsys * pointer to this state - since the subsystem is * newly registered, all tasks and hence the * init_css_set is in the subsystem's root cgroup. */ init_css_set.subsys[ss->id] = css; need_forkexit_callback |= ss->fork || ss->exit; /* At system boot, before all subsystems have been * registered, no tasks have been forked, so we don't * need to invoke fork callbacks here. */ BUG_ON(!list_empty(&init_task.tasks)); BUG_ON(online_css(css)); cgrp_dfl_root.cgrp.subsys_mask |= 1 << ss->id; mutex_unlock(&cgroup_mutex); mutex_unlock(&cgroup_tree_mutex); } /** * cgroup_init_early - cgroup initialization at system boot * * Initialize cgroups at system boot, and initialize any * subsystems that request early init. */ int __init cgroup_init_early(void) { static struct cgroup_sb_opts __initdata opts = { .flags = CGRP_ROOT_SANE_BEHAVIOR }; struct cgroup_subsys *ss; int i; init_cgroup_root(&cgrp_dfl_root, &opts); RCU_INIT_POINTER(init_task.cgroups, &init_css_set); for_each_subsys(ss, i) { WARN(!ss->css_alloc || !ss->css_free || ss->name || ss->id, "invalid cgroup_subsys %d:%s css_alloc=%p css_free=%p name:id=%d:%s\n", i, cgroup_subsys_name[i], ss->css_alloc, ss->css_free, ss->id, ss->name); WARN(strlen(cgroup_subsys_name[i]) > MAX_CGROUP_TYPE_NAMELEN, "cgroup_subsys_name %s too long\n", cgroup_subsys_name[i]); ss->id = i; ss->name = cgroup_subsys_name[i]; if (ss->early_init) cgroup_init_subsys(ss); } return 0; } /** * cgroup_init - cgroup initialization * * Register cgroup filesystem and /proc file, and initialize * any subsystems that didn't request early init. */ int __init cgroup_init(void) { struct cgroup_subsys *ss; unsigned long key; int ssid, err; BUG_ON(cgroup_init_cftypes(NULL, cgroup_base_files)); mutex_lock(&cgroup_tree_mutex); mutex_lock(&cgroup_mutex); /* Add init_css_set to the hash table */ key = css_set_hash(init_css_set.subsys); hash_add(css_set_table, &init_css_set.hlist, key); BUG_ON(cgroup_setup_root(&cgrp_dfl_root, 0)); mutex_unlock(&cgroup_mutex); mutex_unlock(&cgroup_tree_mutex); for_each_subsys(ss, ssid) { if (!ss->early_init) cgroup_init_subsys(ss); /* * cftype registration needs kmalloc and can't be done * during early_init. Register base cftypes separately. */ if (ss->base_cftypes) WARN_ON(cgroup_add_cftypes(ss, ss->base_cftypes)); } cgroup_kobj = kobject_create_and_add("cgroup", fs_kobj); if (!cgroup_kobj) return -ENOMEM; err = register_filesystem(&cgroup_fs_type); if (err < 0) { kobject_put(cgroup_kobj); return err; } proc_create("cgroups", 0, NULL, &proc_cgroupstats_operations); return 0; } static int __init cgroup_wq_init(void) { /* * There isn't much point in executing destruction path in * parallel. Good chunk is serialized with cgroup_mutex anyway. * Use 1 for @max_active. * * We would prefer to do this in cgroup_init() above, but that * is called before init_workqueues(): so leave this until after. */ cgroup_destroy_wq = alloc_workqueue("cgroup_destroy", 0, 1); BUG_ON(!cgroup_destroy_wq); /* * Used to destroy pidlists and separate to serve as flush domain. * Cap @max_active to 1 too. */ cgroup_pidlist_destroy_wq = alloc_workqueue("cgroup_pidlist_destroy", 0, 1); BUG_ON(!cgroup_pidlist_destroy_wq); return 0; } core_initcall(cgroup_wq_init); /* * proc_cgroup_show() * - Print task's cgroup paths into seq_file, one line for each hierarchy * - Used for /proc//cgroup. */ /* TODO: Use a proper seq_file iterator */ int proc_cgroup_show(struct seq_file *m, void *v) { struct pid *pid; struct task_struct *tsk; char *buf, *path; int retval; struct cgroup_root *root; retval = -ENOMEM; buf = kmalloc(PATH_MAX, GFP_KERNEL); if (!buf) goto out; retval = -ESRCH; pid = m->private; tsk = get_pid_task(pid, PIDTYPE_PID); if (!tsk) goto out_free; retval = 0; mutex_lock(&cgroup_mutex); down_read(&css_set_rwsem); for_each_root(root) { struct cgroup_subsys *ss; struct cgroup *cgrp; int ssid, count = 0; if (root == &cgrp_dfl_root && !cgrp_dfl_root_visible) continue; seq_printf(m, "%d:", root->hierarchy_id); for_each_subsys(ss, ssid) if (root->cgrp.subsys_mask & (1 << ssid)) seq_printf(m, "%s%s", count++ ? "," : "", ss->name); if (strlen(root->name)) seq_printf(m, "%sname=%s", count ? "," : "", root->name); seq_putc(m, ':'); cgrp = task_cgroup_from_root(tsk, root); path = cgroup_path(cgrp, buf, PATH_MAX); if (!path) { retval = -ENAMETOOLONG; goto out_unlock; } seq_puts(m, path); seq_putc(m, '\n'); } out_unlock: up_read(&css_set_rwsem); mutex_unlock(&cgroup_mutex); put_task_struct(tsk); out_free: kfree(buf); out: return retval; } /* Display information about each subsystem and each hierarchy */ static int proc_cgroupstats_show(struct seq_file *m, void *v) { struct cgroup_subsys *ss; int i; seq_puts(m, "#subsys_name\thierarchy\tnum_cgroups\tenabled\n"); /* * ideally we don't want subsystems moving around while we do this. * cgroup_mutex is also necessary to guarantee an atomic snapshot of * subsys/hierarchy state. */ mutex_lock(&cgroup_mutex); for_each_subsys(ss, i) seq_printf(m, "%s\t%d\t%d\t%d\n", ss->name, ss->root->hierarchy_id, atomic_read(&ss->root->nr_cgrps), !ss->disabled); mutex_unlock(&cgroup_mutex); return 0; } static int cgroupstats_open(struct inode *inode, struct file *file) { return single_open(file, proc_cgroupstats_show, NULL); } static const struct file_operations proc_cgroupstats_operations = { .open = cgroupstats_open, .read = seq_read, .llseek = seq_lseek, .release = single_release, }; /** * cgroup_fork - initialize cgroup related fields during copy_process() * @child: pointer to task_struct of forking parent process. * * A task is associated with the init_css_set until cgroup_post_fork() * attaches it to the parent's css_set. Empty cg_list indicates that * @child isn't holding reference to its css_set. */ void cgroup_fork(struct task_struct *child) { RCU_INIT_POINTER(child->cgroups, &init_css_set); INIT_LIST_HEAD(&child->cg_list); } /** * cgroup_post_fork - called on a new task after adding it to the task list * @child: the task in question * * Adds the task to the list running through its css_set if necessary and * call the subsystem fork() callbacks. Has to be after the task is * visible on the task list in case we race with the first call to * cgroup_task_iter_start() - to guarantee that the new task ends up on its * list. */ void cgroup_post_fork(struct task_struct *child) { struct cgroup_subsys *ss; int i; /* * This may race against cgroup_enable_task_cg_links(). As that * function sets use_task_css_set_links before grabbing * tasklist_lock and we just went through tasklist_lock to add * @child, it's guaranteed that either we see the set * use_task_css_set_links or cgroup_enable_task_cg_lists() sees * @child during its iteration. * * If we won the race, @child is associated with %current's * css_set. Grabbing css_set_rwsem guarantees both that the * association is stable, and, on completion of the parent's * migration, @child is visible in the source of migration or * already in the destination cgroup. This guarantee is necessary * when implementing operations which need to migrate all tasks of * a cgroup to another. * * Note that if we lose to cgroup_enable_task_cg_links(), @child * will remain in init_css_set. This is safe because all tasks are * in the init_css_set before cg_links is enabled and there's no * operation which transfers all tasks out of init_css_set. */ if (use_task_css_set_links) { struct css_set *cset; down_write(&css_set_rwsem); cset = task_css_set(current); if (list_empty(&child->cg_list)) { rcu_assign_pointer(child->cgroups, cset); list_add(&child->cg_list, &cset->tasks); get_css_set(cset); } up_write(&css_set_rwsem); } /* * Call ss->fork(). This must happen after @child is linked on * css_set; otherwise, @child might change state between ->fork() * and addition to css_set. */ if (need_forkexit_callback) { for_each_subsys(ss, i) if (ss->fork) ss->fork(child); } } /** * cgroup_exit - detach cgroup from exiting task * @tsk: pointer to task_struct of exiting process * @run_callback: run exit callbacks? * * Description: Detach cgroup from @tsk and release it. * * Note that cgroups marked notify_on_release force every task in * them to take the global cgroup_mutex mutex when exiting. * This could impact scaling on very large systems. Be reluctant to * use notify_on_release cgroups where very high task exit scaling * is required on large systems. * * We set the exiting tasks cgroup to the root cgroup (top_cgroup). We * call cgroup_exit() while the task is still competent to handle * notify_on_release(), then leave the task attached to the root cgroup in * each hierarchy for the remainder of its exit. No need to bother with * init_css_set refcnting. init_css_set never goes away and we can't race * with migration path - either PF_EXITING is visible to migration path or * @tsk never got on the tasklist. */ void cgroup_exit(struct task_struct *tsk, int run_callbacks) { struct cgroup_subsys *ss; struct css_set *cset; bool put_cset = false; int i; /* * Unlink from @tsk from its css_set. As migration path can't race * with us, we can check cg_list without grabbing css_set_rwsem. */ if (!list_empty(&tsk->cg_list)) { down_write(&css_set_rwsem); list_del_init(&tsk->cg_list); up_write(&css_set_rwsem); put_cset = true; } /* Reassign the task to the init_css_set. */ cset = task_css_set(tsk); RCU_INIT_POINTER(tsk->cgroups, &init_css_set); if (run_callbacks && need_forkexit_callback) { /* see cgroup_post_fork() for details */ for_each_subsys(ss, i) { if (ss->exit) { struct cgroup_subsys_state *old_css = cset->subsys[i]; struct cgroup_subsys_state *css = task_css(tsk, i); ss->exit(css, old_css, tsk); } } } if (put_cset) put_css_set(cset, true); } static void check_for_release(struct cgroup *cgrp) { if (cgroup_is_releasable(cgrp) && list_empty(&cgrp->cset_links) && list_empty(&cgrp->children)) { /* * Control Group is currently removeable. If it's not * already queued for a userspace notification, queue * it now */ int need_schedule_work = 0; raw_spin_lock(&release_list_lock); if (!cgroup_is_dead(cgrp) && list_empty(&cgrp->release_list)) { list_add(&cgrp->release_list, &release_list); need_schedule_work = 1; } raw_spin_unlock(&release_list_lock); if (need_schedule_work) schedule_work(&release_agent_work); } } /* * Notify userspace when a cgroup is released, by running the * configured release agent with the name of the cgroup (path * relative to the root of cgroup file system) as the argument. * * Most likely, this user command will try to rmdir this cgroup. * * This races with the possibility that some other task will be * attached to this cgroup before it is removed, or that some other * user task will 'mkdir' a child cgroup of this cgroup. That's ok. * The presumed 'rmdir' will fail quietly if this cgroup is no longer * unused, and this cgroup will be reprieved from its death sentence, * to continue to serve a useful existence. Next time it's released, * we will get notified again, if it still has 'notify_on_release' set. * * The final arg to call_usermodehelper() is UMH_WAIT_EXEC, which * means only wait until the task is successfully execve()'d. The * separate release agent task is forked by call_usermodehelper(), * then control in this thread returns here, without waiting for the * release agent task. We don't bother to wait because the caller of * this routine has no use for the exit status of the release agent * task, so no sense holding our caller up for that. */ static void cgroup_release_agent(struct work_struct *work) { BUG_ON(work != &release_agent_work); mutex_lock(&cgroup_mutex); raw_spin_lock(&release_list_lock); while (!list_empty(&release_list)) { char *argv[3], *envp[3]; int i; char *pathbuf = NULL, *agentbuf = NULL, *path; struct cgroup *cgrp = list_entry(release_list.next, struct cgroup, release_list); list_del_init(&cgrp->release_list); raw_spin_unlock(&release_list_lock); pathbuf = kmalloc(PATH_MAX, GFP_KERNEL); if (!pathbuf) goto continue_free; path = cgroup_path(cgrp, pathbuf, PATH_MAX); if (!path) goto continue_free; agentbuf = kstrdup(cgrp->root->release_agent_path, GFP_KERNEL); if (!agentbuf) goto continue_free; i = 0; argv[i++] = agentbuf; argv[i++] = path; argv[i] = NULL; i = 0; /* minimal command environment */ envp[i++] = "HOME=/"; envp[i++] = "PATH=/sbin:/bin:/usr/sbin:/usr/bin"; envp[i] = NULL; /* Drop the lock while we invoke the usermode helper, * since the exec could involve hitting disk and hence * be a slow process */ mutex_unlock(&cgroup_mutex); call_usermodehelper(argv[0], argv, envp, UMH_WAIT_EXEC); mutex_lock(&cgroup_mutex); continue_free: kfree(pathbuf); kfree(agentbuf); raw_spin_lock(&release_list_lock); } raw_spin_unlock(&release_list_lock); mutex_unlock(&cgroup_mutex); } static int __init cgroup_disable(char *str) { struct cgroup_subsys *ss; char *token; int i; while ((token = strsep(&str, ",")) != NULL) { if (!*token) continue; for_each_subsys(ss, i) { if (!strcmp(token, ss->name)) { ss->disabled = 1; printk(KERN_INFO "Disabling %s control group" " subsystem\n", ss->name); break; } } } return 1; } __setup("cgroup_disable=", cgroup_disable); /** * css_tryget_from_dir - get corresponding css from the dentry of a cgroup dir * @dentry: directory dentry of interest * @ss: subsystem of interest * * If @dentry is a directory for a cgroup which has @ss enabled on it, try * to get the corresponding css and return it. If such css doesn't exist * or can't be pinned, an ERR_PTR value is returned. */ struct cgroup_subsys_state *css_tryget_from_dir(struct dentry *dentry, struct cgroup_subsys *ss) { struct kernfs_node *kn = kernfs_node_from_dentry(dentry); struct cgroup_subsys_state *css = NULL; struct cgroup *cgrp; /* is @dentry a cgroup dir? */ if (dentry->d_sb->s_type != &cgroup_fs_type || !kn || kernfs_type(kn) != KERNFS_DIR) return ERR_PTR(-EBADF); rcu_read_lock(); /* * This path doesn't originate from kernfs and @kn could already * have been or be removed at any point. @kn->priv is RCU * protected for this access. See destroy_locked() for details. */ cgrp = rcu_dereference(kn->priv); if (cgrp) css = cgroup_css(cgrp, ss); if (!css || !css_tryget(css)) css = ERR_PTR(-ENOENT); rcu_read_unlock(); return css; } /** * css_from_id - lookup css by id * @id: the cgroup id * @ss: cgroup subsys to be looked into * * Returns the css if there's valid one with @id, otherwise returns NULL. * Should be called under rcu_read_lock(). */ struct cgroup_subsys_state *css_from_id(int id, struct cgroup_subsys *ss) { struct cgroup *cgrp; cgroup_assert_mutexes_or_rcu_locked(); cgrp = idr_find(&ss->root->cgroup_idr, id); if (cgrp) return cgroup_css(cgrp, ss); return NULL; } #ifdef CONFIG_CGROUP_DEBUG static struct cgroup_subsys_state * debug_css_alloc(struct cgroup_subsys_state *parent_css) { struct cgroup_subsys_state *css = kzalloc(sizeof(*css), GFP_KERNEL); if (!css) return ERR_PTR(-ENOMEM); return css; } static void debug_css_free(struct cgroup_subsys_state *css) { kfree(css); } static u64 debug_taskcount_read(struct cgroup_subsys_state *css, struct cftype *cft) { return cgroup_task_count(css->cgroup); } static u64 current_css_set_read(struct cgroup_subsys_state *css, struct cftype *cft) { return (u64)(unsigned long)current->cgroups; } static u64 current_css_set_refcount_read(struct cgroup_subsys_state *css, struct cftype *cft) { u64 count; rcu_read_lock(); count = atomic_read(&task_css_set(current)->refcount); rcu_read_unlock(); return count; } static int current_css_set_cg_links_read(struct seq_file *seq, void *v) { struct cgrp_cset_link *link; struct css_set *cset; char *name_buf; name_buf = kmalloc(NAME_MAX + 1, GFP_KERNEL); if (!name_buf) return -ENOMEM; down_read(&css_set_rwsem); rcu_read_lock(); cset = rcu_dereference(current->cgroups); list_for_each_entry(link, &cset->cgrp_links, cgrp_link) { struct cgroup *c = link->cgrp; cgroup_name(c, name_buf, NAME_MAX + 1); seq_printf(seq, "Root %d group %s\n", c->root->hierarchy_id, name_buf); } rcu_read_unlock(); up_read(&css_set_rwsem); kfree(name_buf); return 0; } #define MAX_TASKS_SHOWN_PER_CSS 25 static int cgroup_css_links_read(struct seq_file *seq, void *v) { struct cgroup_subsys_state *css = seq_css(seq); struct cgrp_cset_link *link; down_read(&css_set_rwsem); list_for_each_entry(link, &css->cgroup->cset_links, cset_link) { struct css_set *cset = link->cset; struct task_struct *task; int count = 0; seq_printf(seq, "css_set %p\n", cset); list_for_each_entry(task, &cset->tasks, cg_list) { if (count++ > MAX_TASKS_SHOWN_PER_CSS) goto overflow; seq_printf(seq, " task %d\n", task_pid_vnr(task)); } list_for_each_entry(task, &cset->mg_tasks, cg_list) { if (count++ > MAX_TASKS_SHOWN_PER_CSS) goto overflow; seq_printf(seq, " task %d\n", task_pid_vnr(task)); } continue; overflow: seq_puts(seq, " ...\n"); } up_read(&css_set_rwsem); return 0; } static u64 releasable_read(struct cgroup_subsys_state *css, struct cftype *cft) { return test_bit(CGRP_RELEASABLE, &css->cgroup->flags); } static struct cftype debug_files[] = { { .name = "taskcount", .read_u64 = debug_taskcount_read, }, { .name = "current_css_set", .read_u64 = current_css_set_read, }, { .name = "current_css_set_refcount", .read_u64 = current_css_set_refcount_read, }, { .name = "current_css_set_cg_links", .seq_show = current_css_set_cg_links_read, }, { .name = "cgroup_css_links", .seq_show = cgroup_css_links_read, }, { .name = "releasable", .read_u64 = releasable_read, }, { } /* terminate */ }; struct cgroup_subsys debug_cgrp_subsys = { .css_alloc = debug_css_alloc, .css_free = debug_css_free, .base_cftypes = debug_files, }; #endif /* CONFIG_CGROUP_DEBUG */