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Message-Id: <20130304033714.130705521@decadent.org.uk>
Date: Mon, 04 Mar 2013 03:38:14 +0000
From: Ben Hutchings <ben@...adent.org.uk>
To: linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc: akpm@...ux-foundation.org, Li Zefan <lizefan@...wei.com>,
Tejun Heo <tj@...nel.org>
Subject: [ 067/153] cgroup: fix exit() vs rmdir() race
3.2-stable review patch. If anyone has any objections, please let me know.
------------------
From: Li Zefan <lizefan@...wei.com>
commit 71b5707e119653039e6e95213f00479668c79b75 upstream.
In cgroup_exit() put_css_set_taskexit() is called without any lock,
which might lead to accessing a freed cgroup:
thread1 thread2
---------------------------------------------
exit()
cgroup_exit()
put_css_set_taskexit()
atomic_dec(cgrp->count);
rmdir();
/* not safe !! */
check_for_release(cgrp);
rcu_read_lock() can be used to make sure the cgroup is alive.
Signed-off-by: Li Zefan <lizefan@...wei.com>
Signed-off-by: Tejun Heo <tj@...nel.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
kernel/cgroup.c | 8 ++++++++
1 file changed, 8 insertions(+)
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -361,12 +361,20 @@ static void __put_css_set(struct css_set
struct cgroup *cgrp = link->cgrp;
list_del(&link->cg_link_list);
list_del(&link->cgrp_link_list);
+
+ /*
+ * We may not be holding cgroup_mutex, and if cgrp->count is
+ * dropped to 0 the cgroup can be destroyed at any time, hence
+ * rcu_read_lock is used to keep it alive.
+ */
+ rcu_read_lock();
if (atomic_dec_and_test(&cgrp->count) &&
notify_on_release(cgrp)) {
if (taskexit)
set_bit(CGRP_RELEASABLE, &cgrp->flags);
check_for_release(cgrp);
}
+ rcu_read_unlock();
kfree(link);
}
--
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