linux-kernel - [PATCH 5/9] cgroup: move cgroup->sibling unlinking to cgroup

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Message-Id: <1399670015-23463-6-git-send-email-tj@kernel.org>
Date:	Fri,  9 May 2014 17:13:31 -0400
From:	Tejun Heo <tj@...nel.org>
To:	lizefan@...wei.com
Cc:	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
	Tejun Heo <tj@...nel.org>
Subject: [PATCH 5/9] cgroup: move cgroup->sibling unlinking to cgroup_put()

Move cgroup->sibling unlinking from cgroup_destroy_css_killed() to
cgroup_put().  This is later but still before the RCU grace period, so
it doesn't break css_next_child() although there now is a larger
window in which a dead cgroup is visible during css iteration.  As css
iteration always could have included offline csses, this doesn't
affect correctness; however, it does make css_next_child() fall back
to reiterting mode more often.  This also makes cgroup_put() directly
take cgroup_mutex, which limits where it can be called from.  These
are not immediately problematic and will be dealt with later.

This change enables simplification of cgroup destruction path.

Signed-off-by: Tejun Heo <tj@...nel.org>
---
 kernel/cgroup.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 45149b7..87ea2ce 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1056,6 +1056,11 @@ static void cgroup_put(struct cgroup *cgrp)
 	if (WARN_ON_ONCE(cgrp->parent && !cgroup_is_dead(cgrp)))
 		return;

+	/* delete this cgroup from parent->children */
+	mutex_lock(&cgroup_mutex);
+	list_del_rcu(&cgrp->sibling);
+	mutex_unlock(&cgroup_mutex);
+
 	cgroup_idr_remove(&cgrp->root->cgroup_idr, cgrp->id);
 	cgrp->id = -1;

@@ -4560,9 +4565,6 @@ static void cgroup_destroy_css_killed(struct cgroup *cgrp)
 {
 	lockdep_assert_held(&cgroup_mutex);

-	/* delete this cgroup from parent->children */
-	list_del_rcu(&cgrp->sibling);
-
 	cgroup_put(cgrp);
 }

-- 
1.9.0

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