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cgroup: introduce cancel_attach()

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Add cancel_attach() operation to struct cgroup_subsys.  cancel_attach()
can be used when can_attach() operation prepares something for the subsys,
but we should rollback what can_attach() operation has prepared if attach
task fails after we've succeeded in can_attach().

Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Acked-by: Li Zefan <lizf@cn.fujitsu.com>
Reviewed-by: Paul Menage <menage@google.com>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Daisuke Nishimura 2010-03-10 15:22:03 -08:00 committed by Linus Torvalds
parent 5ce9f07bf1
commit 2468c7234b
3 changed files with 47 additions and 8 deletions
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13
Documentation/cgroups/cgroups.txt
View file

@ -536,10 +536,21 @@ returns an error, this will abort the attach operation. If a NULL
task is passed, then a successful result indicates that *any*
unspecified task can be moved into the cgroup. Note that this isn't
called on a fork. If this method returns 0 (success) then this should
remain valid while the caller holds cgroup_mutex. If threadgroup is
remain valid while the caller holds cgroup_mutex and it is ensured that either
attach() or cancel_attach() will be called in future. If threadgroup is
true, then a successful result indicates that all threads in the given
thread's threadgroup can be moved together.
void cancel_attach(struct cgroup_subsys *ss, struct cgroup *cgrp,
struct task_struct *task, bool threadgroup)
(cgroup_mutex held by caller)
Called when a task attach operation has failed after can_attach() has succeeded.
A subsystem whose can_attach() has some side-effects should provide this
function, so that the subsytem can implement a rollback. If not, not necessary.
This will be called only about subsystems whose can_attach() operation have
succeeded.
void attach(struct cgroup_subsys *ss, struct cgroup *cgrp,
struct cgroup *old_cgrp, struct task_struct *task,
bool threadgroup)

2
include/linux/cgroup.h
View file

@ -428,6 +428,8 @@ struct cgroup_subsys {
void (*destroy)(struct cgroup_subsys *ss, struct cgroup *cgrp);
int (*can_attach)(struct cgroup_subsys *ss, struct cgroup *cgrp,
struct task_struct *tsk, bool threadgroup);
void (*cancel_attach)(struct cgroup_subsys *ss, struct cgroup *cgrp,
struct task_struct *tsk, bool threadgroup);
void (*attach)(struct cgroup_subsys *ss, struct cgroup *cgrp,
struct cgroup *old_cgrp, struct task_struct *tsk,
bool threadgroup);

40
kernel/cgroup.c
View file

@ -1554,7 +1554,7 @@ int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen)
int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
{
int retval = 0;
struct cgroup_subsys *ss;
struct cgroup_subsys *ss, *failed_ss = NULL;
struct cgroup *oldcgrp;
struct css_set *cg;
struct css_set *newcg;
@ -1568,8 +1568,16 @@ int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
for_each_subsys(root, ss) {
if (ss->can_attach) {
retval = ss->can_attach(ss, cgrp, tsk, false);
if (retval)
return retval;
if (retval) {
/*
* Remember on which subsystem the can_attach()
* failed, so that we only call cancel_attach()
* against the subsystems whose can_attach()
* succeeded. (See below)
*/
failed_ss = ss;
goto out;
}
}
}
@ -1583,14 +1591,17 @@ int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
*/
newcg = find_css_set(cg, cgrp);
put_css_set(cg);
if (!newcg)
return -ENOMEM;
if (!newcg) {
retval = -ENOMEM;
goto out;
}
task_lock(tsk);
if (tsk->flags & PF_EXITING) {
task_unlock(tsk);
put_css_set(newcg);
return -ESRCH;
retval = -ESRCH;
goto out;
}
rcu_assign_pointer(tsk->cgroups, newcg);
task_unlock(tsk);
@ -1616,7 +1627,22 @@ int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
* is no longer empty.
*/
cgroup_wakeup_rmdir_waiter(cgrp);
return 0;
out:
if (retval) {
for_each_subsys(root, ss) {
if (ss == failed_ss)
/*
* This subsystem was the one that failed the
* can_attach() check earlier, so we don't need
* to call cancel_attach() against it or any
* remaining subsystems.
*/
break;
if (ss->cancel_attach)
ss->cancel_attach(ss, cgrp, tsk, false);
}
}
return retval;
}
/*