From: Andrew Morton <akpm@linux-foundation.org>
To: miaox@cn.fujitsu.com
Cc: Paul Menage <menage@google.com>,
Lai Jiangshan <laijs@cn.fujitsu.com>,
Max Krasnyansky <maxk@qualcomm.com>,
Linux-Kernel <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@elte.hu>
Subject: Re: [RESEND][PATCH] cpuset: fix possible deadlock in async_rebuild_sched_domains
Date: Mon, 26 Jan 2009 20:03:07 -0800 [thread overview]
Message-ID: <20090126200307.833b087a.akpm@linux-foundation.org> (raw)
In-Reply-To: <497540BE.4070408@cn.fujitsu.com>
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>
prev parent reply other threads:[~2009-01-27 4:04 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-01-20 3:10 [RESEND][PATCH] cpuset: fix possible deadlock in async_rebuild_sched_domains Miao Xie
2009-01-20 7:24 ` Ingo Molnar
2009-01-27 4:03 ` Andrew Morton [this message]
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