Commit f90d4118 authored Jan 16, 2009 by Miao Xie Committed by Ingo Molnar Jan 19, 2009

cpuset: fix possible deadlock in async_rebuild_sched_domains



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>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

parent f3b8436a

kernel/cpuset.c

+12 −1

Original line number	Diff line number	Diff line
		@@ -60,6 +60,14 @@
		#include <linux/workqueue.h>
		#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
		@@ -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);
		}

		/**

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