Commit 77efecd9 authored Jan 07, 2009 by Lai Jiangshan Committed by Linus Torvalds Jan 08, 2009

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>

parent 104cbd55

kernel/cgroup.c

+6 −1

Original line number	Diff line number	Diff line
		@@ -1214,7 +1214,7 @@ int cgroup_attach_task(struct cgroup cgrp, struct task_struct tsk)
		int retval = 0;
		struct cgroup_subsys *ss;
		struct cgroup *oldcgrp;
		struct css_set *cg = tsk->cgroups;
		struct css_set *cg;
		struct css_set *newcg;
		struct cgroupfs_root *root = cgrp->root;
		int subsys_id;
		@@ -1234,11 +1234,16 @@ int cgroup_attach_task(struct cgroup cgrp, struct task_struct tsk)
		}
		}

		task_lock(tsk);
		cg = tsk->cgroups;
		get_css_set(cg);
		task_unlock(tsk);
		/*
		* Locate or allocate a new css_set for this task,
		* based on its final set of cgroups
		*/
		newcg = find_css_set(cg, cgrp);
		put_css_set(cg);
		if (!newcg)
		return -ENOMEM;