[189/270] cgroup: notify_on_release may not be triggered in some cases

Message ID 1353949160-26803-190-git-send-email-herton.krzesinski@canonical.com
State New
Headers show

Commit Message

Herton Ronaldo Krzesinski Nov. 26, 2012, 4:57 p.m.
3.5.7u1 -stable review patch.  If anyone has any objections, please let me know.


From: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>

commit 1f5320d5972aa50d3e8d2b227b636b370e608359 upstream.

notify_on_release must be triggered when the last process in a cgroup is
move to another. But if the first(and only) process in a cgroup is moved to
another, notify_on_release is not triggered.

	# mkdir /cgroup/cpu/SRC
	# mkdir /cgroup/cpu/DST
	# echo 1 >/cgroup/cpu/SRC/notify_on_release
	# echo 1 >/cgroup/cpu/DST/notify_on_release
	# sleep 300 &
	[1] 8629
	# echo 8629 >/cgroup/cpu/SRC/tasks
	# echo 8629 >/cgroup/cpu/DST/tasks
	-> notify_on_release for /SRC must be triggered at this point,
	   but it isn't.

This is because put_css_set() is called before setting CGRP_RELEASABLE
in cgroup_task_migrate(), and is a regression introduce by the
commit:74a1166d(cgroups: make procs file writable), which was merged
into v3.0.

Cc: Ben Blum <bblum@andrew.cmu.edu>
Acked-by: Li Zefan <lizefan@huawei.com>
Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Herton Ronaldo Krzesinski <herton.krzesinski@canonical.com>
 kernel/cgroup.c |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)


diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 15462a0..63c9596 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1927,9 +1927,8 @@  static void cgroup_task_migrate(struct cgroup *cgrp, struct cgroup *oldcgrp,
 	 * trading it for newcg is protected by cgroup_mutex, we're safe to drop
 	 * it here; it will be freed under RCU.
-	put_css_set(oldcg);
 	set_bit(CGRP_RELEASABLE, &oldcgrp->flags);
+	put_css_set(oldcg);