cgroup: make sure a parent css isn't offlined before its children
authorTejun Heo <tj@kernel.org>
Thu, 21 Jan 2016 20:31:11 +0000 (15:31 -0500)
committerTejun Heo <tj@kernel.org>
Fri, 22 Jan 2016 15:42:57 +0000 (10:42 -0500)
commitaa226ff4a1ce79f229c6b7a4c0a14e17fececd01
tree1db4c5f20ffafca177de0bbe26beddcc60e26f93
parente93ad19d05648397ef3bcb838d26aec06c245dc0
cgroup: make sure a parent css isn't offlined before its children

There are three subsystem callbacks in css shutdown path -
css_offline(), css_released() and css_free().  Except for
css_released(), cgroup core didn't guarantee the order of invocation.
css_offline() or css_free() could be called on a parent css before its
children.  This behavior is unexpected and led to bugs in cpu and
memory controller.

This patch updates offline path so that a parent css is never offlined
before its children.  Each css keeps online_cnt which reaches zero iff
itself and all its children are offline and offline_css() is invoked
only after online_cnt reaches zero.

This fixes the memory controller bug and allows the fix for cpu
controller.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-and-tested-by: Christian Borntraeger <borntraeger@de.ibm.com>
Reported-by: Brian Christiansen <brian.o.christiansen@gmail.com>
Link: http://lkml.kernel.org/g/5698A023.9070703@de.ibm.com
Link: http://lkml.kernel.org/g/CAKB58ikDkzc8REt31WBkD99+hxNzjK4+FBmhkgS+NVrC9vjMSg@mail.gmail.com
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org
include/linux/cgroup-defs.h
kernel/cgroup.c