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cgroup: remove cgroup_lock_is_held()

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We don't want controllers to assume that the information is officially
available and do funky things with it.

The only user is task_subsys_state_check() which uses it to verify RCU
access context.  We can move cgroup_lock_is_held() inside
CONFIG_PROVE_RCU but that doesn't add meaningful protection compared
to conditionally exposing cgroup_mutex.

Remove cgroup_lock_is_held(), export cgroup_mutex iff CONFIG_PROVE_RCU
and use lockdep_is_held() directly on the mutex in
task_subsys_state_check().

While at it, add parentheses around macro arguments in
task_subsys_state_check().

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
This commit is contained in:
Tejun Heo 2013-04-07 09:29:51 -07:00
parent 47cfcd0922
commit 2219449a65
2 changed files with 15 additions and 18 deletions
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13
include/linux/cgroup.h
View file

@ -30,7 +30,6 @@ struct css_id;
extern int cgroup_init_early(void);
extern int cgroup_init(void);
extern int cgroup_lock_is_held(void);
extern void cgroup_fork(struct task_struct *p);
extern void cgroup_post_fork(struct task_struct *p);
extern void cgroup_exit(struct task_struct *p, int run_callbacks);
@ -552,10 +551,16 @@ static inline struct cgroup_subsys_state *cgroup_subsys_state(
* rcu_dereference_check() conditions, such as locks used during the
* cgroup_subsys::attach() methods.
*/
#ifdef CONFIG_PROVE_RCU
extern struct mutex cgroup_mutex;
#define task_subsys_state_check(task, subsys_id, __c) \
rcu_dereference_check(task->cgroups->subsys[subsys_id], \
lockdep_is_held(&task->alloc_lock) || \
cgroup_lock_is_held() || (__c))
rcu_dereference_check((task)->cgroups->subsys[(subsys_id)], \
lockdep_is_held(&(task)->alloc_lock) || \
lockdep_is_held(&cgroup_mutex) || (__c))
#else
#define task_subsys_state_check(task, subsys_id, __c) \
rcu_dereference((task)->cgroups->subsys[(subsys_id)])
#endif
static inline struct cgroup_subsys_state *
task_subsys_state(struct task_struct *task, int subsys_id)

20
kernel/cgroup.c
View file

@ -83,7 +83,13 @@
* B happens only through cgroup_show_options() and using cgroup_root_mutex
* breaks it.
*/
#ifdef CONFIG_PROVE_RCU
DEFINE_MUTEX(cgroup_mutex);
EXPORT_SYMBOL_GPL(cgroup_mutex); /* only for task_subsys_state_check() */
#else
static DEFINE_MUTEX(cgroup_mutex);
#endif
static DEFINE_MUTEX(cgroup_root_mutex);
/*
@ -251,20 +257,6 @@ static int cgroup_destroy_locked(struct cgroup *cgrp);
static int cgroup_addrm_files(struct cgroup *cgrp, struct cgroup_subsys *subsys,
struct cftype cfts[], bool is_add);
#ifdef CONFIG_PROVE_LOCKING
int cgroup_lock_is_held(void)
{
return lockdep_is_held(&cgroup_mutex);
}
#else /* #ifdef CONFIG_PROVE_LOCKING */
int cgroup_lock_is_held(void)
{
return mutex_is_locked(&cgroup_mutex);
}
#endif /* #else #ifdef CONFIG_PROVE_LOCKING */
EXPORT_SYMBOL_GPL(cgroup_lock_is_held);
static int css_unbias_refcnt(int refcnt)
{
return refcnt >= 0 ? refcnt : refcnt - CSS_DEACT_BIAS;