From 58b79a91f57efec9457de8ff93a4cc4fb8daf753 Mon Sep 17 00:00:00 2001
From: Tejun Heo <tj@kernel.org>
Date: Fri, 6 Sep 2013 15:31:08 -0400
Subject: [PATCH 1/2] cgroup: fix cgroup post-order descendant walk of empty
subtree
bd8815a6d8 ("cgroup: make css_for_each_descendant() and friends
include the origin css in the iteration") updated cgroup descendant
iterators to include the origin css; unfortuantely, it forgot to drop
special case handling in css_next_descendant_post() for empty subtree
leading to failure to visit the origin css without any child.
Fix it by dropping the special case handling and always returning the
leftmost descendant on the first iteration.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
---
kernel/cgroup.c | 8 +++-----
1 file changed, 3 insertions(+), 5 deletions(-)
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index e0aeb32415ff..8075b72d22be 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -3187,11 +3187,9 @@ css_next_descendant_post(struct cgroup_subsys_state *pos,
WARN_ON_ONCE(!rcu_read_lock_held());
- /* if first iteration, visit the leftmost descendant */
- if (!pos) {
- next = css_leftmost_descendant(root);
- return next != root ? next : NULL;
- }
+ /* if first iteration, visit leftmost descendant which may be @root */
+ if (!pos)
+ return css_leftmost_descendant(root);
/* if we visited @root, we're done */
if (pos == root)
From ea84753c98a7ac6b74e530b64c444a912b3835ca Mon Sep 17 00:00:00 2001
From: Anjana V Kumar <anjanavk12@gmail.com>
Date: Sat, 12 Oct 2013 10:59:17 +0800
Subject: [PATCH 2/2] cgroup: fix to break the while loop in
cgroup_attach_task() correctly
Both Anjana and Eunki reported a stall in the while_each_thread loop
in cgroup_attach_task().
It's because, when we attach a single thread to a cgroup, if the cgroup
is exiting or is already in that cgroup, we won't break the loop.
If the task is already in the cgroup, the bug can lead to another thread
being attached to the cgroup unexpectedly:
# echo 5207 > tasks
# cat tasks
5207
# echo 5207 > tasks
# cat tasks
5207
5215
What's worse, if the task to be attached isn't the leader of the thread
group, we might never exit the loop, hence cpu stall. Thanks for Oleg's
analysis.
This bug was introduced by commit 081aa458c38ba576bdd4265fc807fa95b48b9e79
("cgroup: consolidate cgroup_attach_task() and cgroup_attach_proc()")
[ lizf: - fixed the first continue, pointed out by Oleg,
- rewrote changelog. ]
Cc: <stable@vger.kernel.org> # 3.9+
Reported-by: Eunki Kim <eunki_kim@samsung.com>
Reported-by: Anjana V Kumar <anjanavk12@gmail.com>
Signed-off-by: Anjana V Kumar <anjanavk12@gmail.com>
Signed-off-by: Li Zefan <lizefan@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
---
kernel/cgroup.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 8075b72d22be..1bf4f7a12703 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -2038,7 +2038,7 @@ static int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk,
/* @tsk either already exited or can't exit until the end */
if (tsk->flags & PF_EXITING)
- continue;
+ goto next;
/* as per above, nr_threads may decrease, but not increase. */
BUG_ON(i >= group_size);
@@ -2046,7 +2046,7 @@ static int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk,
ent.cgrp = task_cgroup_from_root(tsk, root);
/* nothing to do if this task is already in the cgroup */
if (ent.cgrp == cgrp)
- continue;
+ goto next;
/*
* saying GFP_ATOMIC has no effect here because we did prealloc
* earlier, but it's good form to communicate our expectations.
@@ -2054,7 +2054,7 @@ static int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk,
retval = flex_array_put(group, i, &ent, GFP_ATOMIC);
BUG_ON(retval != 0);
i++;
-
+ next:
if (!threadgroup)
break;
} while_each_thread(leader, tsk);