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authorTejun Heo <tj@kernel.org>2013-05-24 10:50:24 +0900
committerTejun Heo <tj@kernel.org>2013-05-24 10:50:24 +0900
commit7805d000db30a3787a4c969bab6ae4d8a5fd8ce6 (patch)
tree5178e1adaa4f398d2c1367fb38633191e81764e5 /kernel
parentd6cbf35dac8a3dadb9103379820c96d7c85df3d9 (diff)
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cgroup: fix a subtle bug in descendant pre-order walk
When cgroup_next_descendant_pre() initiates a walk, it checks whether the subtree root doesn't have any children and if not returns NULL. Later code assumes that the subtree isn't empty. This is broken because the subtree may become empty inbetween, which can lead to the traversal escaping the subtree by walking to the sibling of the subtree root. There's no reason to have the early exit path. Remove it along with the later assumption that the subtree isn't empty. This simplifies the code a bit and fixes the subtle bug. While at it, fix the comment of cgroup_for_each_descendant_pre() which was incorrectly referring to ->css_offline() instead of ->css_online(). Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Michal Hocko <mhocko@suse.cz> Cc: stable@vger.kernel.org
Diffstat (limited to 'kernel')
-rw-r--r--kernel/cgroup.c9
1 files changed, 3 insertions, 6 deletions
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 38b136553044..31e9ef319070 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2954,11 +2954,8 @@ struct cgroup *cgroup_next_descendant_pre(struct cgroup *pos,
WARN_ON_ONCE(!rcu_read_lock_held());
/* if first iteration, pretend we just visited @cgroup */
- if (!pos) {
- if (list_empty(&cgroup->children))
- return NULL;
+ if (!pos)
pos = cgroup;
- }
/* visit the first child if exists */
next = list_first_or_null_rcu(&pos->children, struct cgroup, sibling);
@@ -2966,14 +2963,14 @@ struct cgroup *cgroup_next_descendant_pre(struct cgroup *pos,
return next;
/* no child, visit my or the closest ancestor's next sibling */
- do {
+ while (pos != cgroup) {
next = list_entry_rcu(pos->sibling.next, struct cgroup,
sibling);
if (&next->sibling != &pos->parent->children)
return next;
pos = pos->parent;
- } while (pos != cgroup);
+ }
return NULL;
}