This is a note to let you know that I've just added the patch titled
cpuset: fix a locking issue in cpuset_migrate_mm()
to the 3.13-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:
cpuset-fix-a-locking-issue-in-cpuset_migrate_mm.patch
and it can be found in the queue-3.13 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 4729583006772b9530404bc1bb7c3aa4a10ffd4d Mon Sep 17 00:00:00 2001
From: Li Zefan <lizefan@xxxxxxxxxx>
Date: Thu, 27 Feb 2014 18:19:03 +0800
Subject: cpuset: fix a locking issue in cpuset_migrate_mm()
From: Li Zefan <lizefan@xxxxxxxxxx>
commit 4729583006772b9530404bc1bb7c3aa4a10ffd4d upstream.
I can trigger a lockdep warning:
# mount -t cgroup -o cpuset xxx /cgroup
# mkdir /cgroup/cpuset
# mkdir /cgroup/tmp
# echo 0 > /cgroup/tmp/cpuset.cpus
# echo 0 > /cgroup/tmp/cpuset.mems
# echo 1 > /cgroup/tmp/cpuset.memory_migrate
# echo $$ > /cgroup/tmp/tasks
# echo 1 > /cgruop/tmp/cpuset.mems
===============================
[ INFO: suspicious RCU usage. ]
3.14.0-rc1-0.1-default+ #32 Not tainted
-------------------------------
include/linux/cgroup.h:682 suspicious rcu_dereference_check() usage!
...
[<ffffffff81582174>] dump_stack+0x72/0x86
[<ffffffff810b8f01>] lockdep_rcu_suspicious+0x101/0x140
[<ffffffff81105ba1>] cpuset_migrate_mm+0xb1/0xe0
...
We used to hold cgroup_mutex when calling cpuset_migrate_mm(), but now
we hold cpuset_mutex, which causes task_css() to complain.
This is not a false-positive but a real issue.
Holding cpuset_mutex won't prevent a task from migrating to another
cpuset, and it won't prevent the original task->cgroup from destroying
during this change.
Fixes: 5d21cc2db040 (cpuset: replace cgroup_mutex locking with cpuset internal locking)
Signed-off-by: Li Zefan <lizefan@xxxxxxxxxx>
Sigend-off-by: Tejun Heo <tj@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/cpuset.c | 8 ++------
1 file changed, 2 insertions(+), 6 deletions(-)
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -974,12 +974,6 @@ static int update_cpumask(struct cpuset
* Temporarilly set tasks mems_allowed to target nodes of migration,
* so that the migration code can allocate pages on these nodes.
*
- * Call holding cpuset_mutex, so current's cpuset won't change
- * during this call, as manage_mutex holds off any cpuset_attach()
- * calls. Therefore we don't need to take task_lock around the
- * call to guarantee_online_mems(), as we know no one is changing
- * our task's cpuset.
- *
* While the mm_struct we are migrating is typically from some
* other task, the task_struct mems_allowed that we are hacking
* is for our current task, which must allocate new pages for that
@@ -996,8 +990,10 @@ static void cpuset_migrate_mm(struct mm_
do_migrate_pages(mm, from, to, MPOL_MF_MOVE_ALL);
+ rcu_read_lock();
mems_cs = effective_nodemask_cpuset(task_cs(tsk));
guarantee_online_mems(mems_cs, &tsk->mems_allowed);
+ rcu_read_unlock();
}
/*
Patches currently in stable-queue which might be from lizefan@xxxxxxxxxx are
queue-3.13/cpuset-fix-a-race-condition-in-__cpuset_node_allowed_softwall.patch
queue-3.13/cpuset-fix-a-locking-issue-in-cpuset_migrate_mm.patch
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