From: Lai Jiangshan <laijs@cn.fujitsu.com>
Date: Thu, 8 Jan 2009 02:07:39 +0000 (-0800)
Subject: cgroups: call find_css_set() safely in cgroup_attach_task()
X-Git-Tag: v2.6.29-rc1~149
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=77efecd9e0526327548152df715ab8644ecb5ba0;p=pandora-kernel.git

cgroups: call find_css_set() safely in cgroup_attach_task()

In cgroup_attach_task(), tsk maybe exit when we call find_css_set().  and
find_css_set() will access to invalid css_set.

This patch increases the count before get_css_set(), and decreases it
after find_css_set().

NOTE:

css_set's refcount is also taskcount, after this patch applied, taskcount
may be off-by-one WHEN cgroup_lock() is not held.  but I reviewed other
code which use taskcount, they are still correct.  No regression found by
reviewing and simply testing.

So I do not use two counters in css_set.  (one counter for taskcount, the
other for refcount.  like struct mm_struct) If this fix cause regression,
we will use two counters in css_set.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: Paul Menage <menage@google.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: Balbir Singh <balbir@in.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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