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memcg: let css_get_next() rely upon rcu_read_lock()

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Remove lock and unlock around css_get_next()'s call to idr_get_next().
memcg iterators (only users of css_get_next) already did rcu_read_lock(),
and its comment demands that; but add a WARN_ON_ONCE to make sure of it.

Signed-off-by: Hugh Dickins <hughd@google.com>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: Li Zefan <lizf@cn.fujitsu.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Hugh Dickins 2012-03-21 16:34:21 -07:00 committed by Linus Torvalds
parent 42aee6c495
commit ca464d69b1
1 changed files with 2 additions and 3 deletions
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5
kernel/cgroup.c
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@ -5033,6 +5033,8 @@ css_get_next(struct cgroup_subsys *ss, int id,
return NULL;
BUG_ON(!ss->use_id);
WARN_ON_ONCE(!rcu_read_lock_held());
/* fill start point for scan */
tmpid = id;
while (1) {
@ -5040,10 +5042,7 @@ css_get_next(struct cgroup_subsys *ss, int id,
* scan next entry from bitmap(tree), tmpid is updated after
* idr_get_next().
*/
spin_lock(&ss->id_lock);
tmp = idr_get_next(&ss->idr, &tmpid);
spin_unlock(&ss->id_lock);
if (!tmp)
break;
if (tmp->depth >= depth && tmp->stack[depth] == rootid) {