Commit 2019f634 authored Jan 07, 2009 by Lai Jiangshan Committed by Linus Torvalds Jan 08, 2009

cgroups: fix cgroup_iter_next() bug



We access res->cgroups without the task_lock(), so res->cgroups may be
changed.  it's unreliable, and "if (l == &res->cgroups->tasks)" may be
false forever.

We don't need add any lock for fixing this bug.  we just access to struct
css_set by struct cg_cgroup_link, not by struct task_struct.

Since we hold css_set_lock, struct cg_cgroup_link is reliable.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Reviewed-by: 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 b12b533f

kernel/cgroup.c

+3 −1

Original line number	Diff line number	Diff line
		@@ -1808,6 +1808,7 @@ struct task_struct cgroup_iter_next(struct cgroup cgrp,
		{
		struct task_struct *res;
		struct list_head *l = it->task;
		struct cg_cgroup_link *link;

		/* If the iterator cg is NULL, we have no tasks */
		if (!it->cg_link)
		@@ -1815,7 +1816,8 @@ struct task_struct cgroup_iter_next(struct cgroup cgrp,
		res = list_entry(l, struct task_struct, cg_list);
		/* Advance iterator to find next entry */
		l = l->next;
		if (l == &res->cgroups->tasks) {
		link = list_entry(it->cg_link, struct cg_cgroup_link, cgrp_link_list);
		if (l == &link->cg->tasks) {
		/* We reached the end of this task list - move on to
		* the next cg_cgroup_link */
		cgroup_advance_iter(cgrp, it);