This is a note to let you know that I've just added the patch titled
cgroup: fix exit() vs rmdir() race
to the 3.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
cgroup-fix-exit-vs-rmdir-race.patch
and it can be found in the queue-3.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 71b5707e119653039e6e95213f00479668c79b75 Mon Sep 17 00:00:00 2001
From: Li Zefan <lizefan@xxxxxxxxxx>
Date: Thu, 24 Jan 2013 14:43:28 +0800
Subject: cgroup: fix exit() vs rmdir() race
From: Li Zefan <lizefan@xxxxxxxxxx>
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@xxxxxxxxxx>
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/cgroup.c | 8 ++++++++
1 file changed, 8 insertions(+)
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -378,12 +378,20 @@ 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);
}
Patches currently in stable-queue which might be from lizefan@xxxxxxxxxx are
queue-3.4/cpuset-fix-cpuset_print_task_mems_allowed-vs-rename-race.patch
queue-3.4/cgroup-fix-exit-vs-rmdir-race.patch
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