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cgroup: factor out kill_css()

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Factor out css ref killing from cgroup_destroy_locked() into
kill_css().  We're gonna add more to the path and the factored out
function will eventually be called from other places too.

While at it, replace open coded percpu_ref_get() with css_get() for
consistency.  This shouldn't cause any functional difference as the
function is not used for root cgroups.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
This commit is contained in:
Tejun Heo 2013-08-13 20:22:51 -04:00
parent 09a503ea3a
commit edae0c3358
1 changed files with 35 additions and 23 deletions
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58
kernel/cgroup.c
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@ -4595,6 +4595,36 @@ static void css_killed_ref_fn(struct percpu_ref *ref)
schedule_work(&css->destroy_work);
}
/**
* kill_css - destroy a css
* @css: css to destroy
*
* This function initiates destruction of @css by 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)
{
/*
* 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);
}
/**
* cgroup_destroy_locked - the first stage of cgroup destruction
* @cgrp: cgroup to be destroyed
@ -4641,30 +4671,12 @@ static int cgroup_destroy_locked(struct cgroup *cgrp)
return -EBUSY;
/*
* Block new css_tryget() by killing css refcnts. 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.
* 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.
* 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.
*/
for_each_root_subsys(cgrp->root, ss) {
struct cgroup_subsys_state *css = cgroup_css(cgrp, ss->subsys_id);
/*
* Killing would put the base ref, but we need to keep it
* alive until after ->css_offline.
*/
percpu_ref_get(&css->refcnt);
percpu_ref_kill_and_confirm(&css->refcnt, css_killed_ref_fn);
}
for_each_root_subsys(cgrp->root, ss)
kill_css(cgroup_css(cgrp, ss->subsys_id));
/*
* Mark @cgrp dead. This prevents further task migration and child