From: Lai Jiangshan <laijs@cn.fujitsu.com>
To: Tejun Heo <tj@kernel.org>
Cc: linux-kernel@vger.kernel.org
Subject: Re: [PATCH wq/for-3.6-fixes 3/3] workqueue: fix possible idle worker depletion during CPU_ONLINE
Date: Fri, 07 Sep 2012 11:10:34 +0800 [thread overview]
Message-ID: <504965AA.6090107@cn.fujitsu.com> (raw)
In-Reply-To: <20120906200802.GI29092@google.com>
On 09/07/2012 04:08 AM, Tejun Heo wrote:
>>From 985aafbf530834a9ab16348300adc7cbf35aab76 Mon Sep 17 00:00:00 2001
> From: Tejun Heo <tj@kernel.org>
> Date: Thu, 6 Sep 2012 12:50:41 -0700
>
> To simplify both normal and CPU hotplug paths, while CPU hotplug is in
> progress, manager_mutex is held to prevent one of the workers from
> becoming a manager and creating or destroying workers; unfortunately,
> it currently may lead to idle worker depletion which in turn can lead
> to deadlock under extreme circumstances.
>
> Idle workers aren't allowed to become busy if there's no other idle
> worker left to create more idle workers, but during CPU_ONLINE
> gcwq_associate() is holding all managerships and all the idle workers
> can proceed to become busy before gcwq_associate() is finished.
>
> This patch fixes the bug by releasing manager_mutexes before letting
> the rebound idle workers go. This ensures that by the time idle
> workers check whether management is necessary, CPU_ONLINE already has
> released the positions.
>
Could you review manage_workers_slowpath() in V4 patchset.
It has enough changelog and comments.
After the discussion,
We don't move the hotplug code outside hotplug code. it matches this requirement.
Since we introduce manage_mutex(), any palace should be allowed to grab it
when its context allows. So it is not hotplug code's responsibility of this bug.
manage_workers() just use mutex_trylock() to grab the lock, it does not make
hard to do it jobs when need, and it does not try to find out the reason of fail.
so I think it is manage_workers()'s responsibility to handle this bug.
a manage_workers_slowpath() is enough to fix the bug.
=====
manage_workers_slowpath() just adds a little overhead over manage_workers(),
so we can use manage_workers_slowpath() to replace manage_workers(), thus we
can reduce the code of manage_workers() and we can do more cleanup for manage.
Thanks,
Lai
next prev parent reply other threads:[~2012-09-07 3:09 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-06 20:06 [PATCH wq/for-3.6-fixes 1/3] workqueue: break out gcwq->lock locking from gcwq_claim/release_management_and_[un]lock() Tejun Heo
2012-09-06 20:07 ` [PATCH wq/for-3.6-fixes 2/3] workqueue: rename rebind_workers() to gcwq_associate() and let it handle locking and DISASSOCIATED clearing Tejun Heo
2012-09-06 20:08 ` [PATCH wq/for-3.6-fixes 3/3] workqueue: fix possible idle worker depletion during CPU_ONLINE Tejun Heo
2012-09-07 1:53 ` Lai Jiangshan
2012-09-07 19:25 ` Tejun Heo
2012-09-07 3:10 ` Lai Jiangshan [this message]
2012-09-07 19:29 ` Tejun Heo
2012-09-07 20:22 ` Tejun Heo
2012-09-07 20:34 ` Tejun Heo
2012-09-07 23:05 ` Tejun Heo
2012-09-07 23:07 ` Tejun Heo
2012-09-07 23:41 ` Tejun Heo
2012-09-08 17:18 ` Lai Jiangshan
2012-09-08 17:29 ` Tejun Heo
2012-09-08 17:32 ` Tejun Heo
2012-09-08 17:40 ` Lai Jiangshan
2012-09-08 17:41 ` Tejun Heo
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