[RESEND][PATCH] cpuset: fix possible deadlock in async_rebuild_sched_domains

[RESEND][PATCH] cpuset: fix possible deadlock in async_rebuild_sched_domains

[Miao Xie]

Lockdep reported some possible circular locking info when we tested cpuset on
NUMA/fake NUMA box.

=======================================================
[ INFO: possible circular locking dependency detected ]
2.6.29-rc1-00224-ga652504 #111
-------------------------------------------------------
bash/2968 is trying to acquire lock:
 (events){--..}, at: [<ffffffff8024c8cd>] flush_work+0x24/0xd8

but task is already holding lock:
 (cgroup_mutex){--..}, at: [<ffffffff8026ad1e>] cgroup_lock_live_group+0x12/0x29

which lock already depends on the new lock.
......
-------------------------------------------------------

Steps to reproduce:
# mkdir /dev/cpuset
# mount -t cpuset xxx /dev/cpuset
# mkdir /dev/cpuset/0
# echo 0 > /dev/cpuset/0/cpus
# echo 0 > /dev/cpuset/0/mems
# echo 1 > /dev/cpuset/0/memory_migrate
# cat /dev/zero > /dev/null &
# echo $! > /dev/cpuset/0/tasks

This is because async_rebuild_sched_domains has the following lock sequence:
run_workqueue(async_rebuild_sched_domains)
	-> do_rebuild_sched_domains -> cgroup_lock

But, attaching tasks when memory_migrate is set has following:
cgroup_lock_live_group(cgroup_tasks_write)
	-> do_migrate_pages -> flush_work

This patch fixes it by using a separate workqueue thread.

Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Cc: Max Krasnyansky <maxk@qualcomm.com>
---
 kernel/cpuset.c |   13 ++++++++++++-
 1 files changed, 12 insertions(+), 1 deletions(-)

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index a856788..f76db9d 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -61,6 +61,14 @@
 #include <linux/cgroup.h>
 
 /*
+ * Workqueue for cpuset related tasks.
+ *
+ * Using kevent workqueue may cause deadlock when memory_migrate
+ * is set. So we create a separate workqueue thread for cpuset.
+ */
+static struct workqueue_struct *cpuset_wq;
+
+/*
  * Tracks how many cpusets are currently defined in system.
  * When there is only one cpuset (the root cpuset) we can
  * short circuit some hooks.
@@ -831,7 +839,7 @@ static DECLARE_WORK(rebuild_sched_domains_work, do_rebuild_sched_domains);
  */
 static void async_rebuild_sched_domains(void)
 {
-	schedule_work(&rebuild_sched_domains_work);
+	queue_work(cpuset_wq, &rebuild_sched_domains_work);
 }
 
 /*
@@ -2111,6 +2119,9 @@ void __init cpuset_init_smp(void)
 
 	hotcpu_notifier(cpuset_track_online_cpus, 0);
 	hotplug_memory_notifier(cpuset_track_online_nodes, 10);
+
+	cpuset_wq = create_singlethread_workqueue("cpuset");
+	BUG_ON(!cpuset_wq);
 }
 
 /**
-- 
1.6.0.3

Re: [RESEND][PATCH] cpuset: fix possible deadlock in async_rebuild_sched_domains

[Ingo Molnar]

* Miao Xie <miaox@cn.fujitsu.com> wrote:

> Lockdep reported some possible circular locking info when we tested 
> cpuset on NUMA/fake NUMA box.

I have applied your original patch to tip/sched/urgent two days ago, 
thanks!

	Ingo

Re: [RESEND][PATCH] cpuset: fix possible deadlock in async_rebuild_sched_domains

[Andrew Morton]

On Tue, 20 Jan 2009 11:10:54 +0800 Miao Xie <miaox@cn.fujitsu.com> wrote:

> Lockdep reported some possible circular locking info when we tested cpuset on
> NUMA/fake NUMA box.
> 
> =======================================================
> [ INFO: possible circular locking dependency detected ]
> 2.6.29-rc1-00224-ga652504 #111
> -------------------------------------------------------
> bash/2968 is trying to acquire lock:
>  (events){--..}, at: [<ffffffff8024c8cd>] flush_work+0x24/0xd8
> 
> but task is already holding lock:
>  (cgroup_mutex){--..}, at: [<ffffffff8026ad1e>] cgroup_lock_live_group+0x12/0x29
> 
> which lock already depends on the new lock.
> ......
> -------------------------------------------------------
> 
> Steps to reproduce:
> # mkdir /dev/cpuset
> # mount -t cpuset xxx /dev/cpuset
> # mkdir /dev/cpuset/0
> # echo 0 > /dev/cpuset/0/cpus
> # echo 0 > /dev/cpuset/0/mems
> # echo 1 > /dev/cpuset/0/memory_migrate
> # cat /dev/zero > /dev/null &
> # echo $! > /dev/cpuset/0/tasks
> 
> This is because async_rebuild_sched_domains has the following lock sequence:
> run_workqueue(async_rebuild_sched_domains)
> 	-> do_rebuild_sched_domains -> cgroup_lock
> 
> But, attaching tasks when memory_migrate is set has following:
> cgroup_lock_live_group(cgroup_tasks_write)
> 	-> do_migrate_pages -> flush_work

Where is this flush_work() call?  lru_add_drain_all()->schedule_on_each_cpu()?

If so, and if that is the only such callsite then we could/should
rework this code to use work_on_cpu(), if we manage to fix that thing.

It would be somewhat inefficient.  It would be better if work_on_cpu()
were to take a cpumask argument, and avoid blocking behind each CPU one
at a time.  But first things first.

> This patch fixes it by using a separate workqueue thread.

<wonders when RESERVED_PIDS became a logarithm>