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Commit edae0c33 authored by Tejun Heo's avatar Tejun Heo
Browse files

cgroup: factor out kill_css() 



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: default avatarTejun Heo <tj@kernel.org>
Acked-by: default avatarLi Zefan <lizefan@huawei.com>
parent 09a503ea

kernel/cgroup.c

+35 −23
Original line number Diff line number Diff line
@@ -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