From: Lai Jiangshan <laijs@cn.fujitsu.com>
To: Tejun Heo <tj@kernel.org>
Cc: linux-kernel@vger.kernel.org
Subject: Re: [PATCH 4/9 V3] workqueue: add non_manager_role_manager_mutex_unlock()
Date: Fri, 31 Aug 2012 09:08:22 +0800 [thread overview]
Message-ID: <50400E86.8090500@cn.fujitsu.com> (raw)
In-Reply-To: <20120830091739.GA10874@dhcp-172-17-108-109.mtv.corp.google.com>
On 08/30/2012 05:17 PM, Tejun Heo wrote:
> Hello, Lai.
>
> On Thu, Aug 30, 2012 at 05:16:01PM +0800, Lai Jiangshan wrote:
>> gcwq_unbind_fn() is unsafe even it is called from a work item.
>> so we need non_manager_role_manager_mutex_unlock().
>>
>> If rebind_workers() is called from a work item, it is safe when there is
>> no CPU_INTENSIVE items. but we can't disable CPU_INTENSIVE items,
>> so it is still unsafe, we need non_manager_role_manager_mutex_unlock() too.
>
> Can you please elaborate? Why is it not safe if there are
> CPU_INTENSIVE items?
>
> Thanks.
>
Imaging there only two workers, they all have UNBOUND bit because the rebind_workers()
has not been called. The First one is processing work items, the second one is idle,
when the first one encounter the work item of rebind_workers() and handle it, at the same
the second one try to create workers and failed and go to process work items too.
but unlikely the second one encounters a CPU_INTENSIVE items, the nr_running is still
<=1 after the first one finish rebind_workers().
nr_running.
first one: process work item endless +0 or +1
second one: process the CPU_INTENSIVE item endless +0
No one can service for manager role.
Thanks.
Lai
next prev parent reply other threads:[~2012-08-31 1:06 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-08-29 16:51 [PATCH 0/9 V3] workqueue: fix and cleanup hotplug/rebind_workers() Lai Jiangshan
2012-08-29 16:51 ` [PATCH 1/9 V3] workqueue: ensure the wq_worker_sleeping() see the right flags Lai Jiangshan
2012-08-29 16:51 ` [PATCH 2/9 V3] workqueue: fix deadlock in rebind_workers() Lai Jiangshan
2012-08-29 16:51 ` [PATCH 3/9 V3] workqueue: add POOL_MANAGING_WORKERS Lai Jiangshan
2012-08-29 18:21 ` Tejun Heo
2012-08-30 2:38 ` Lai Jiangshan
2012-08-29 16:51 ` [PATCH 4/9 V3] workqueue: add non_manager_role_manager_mutex_unlock() Lai Jiangshan
2012-08-29 18:25 ` Tejun Heo
2012-08-30 9:16 ` Lai Jiangshan
2012-08-30 9:17 ` Tejun Heo
2012-08-31 1:08 ` Lai Jiangshan [this message]
2012-08-29 16:51 ` [PATCH 5/9 V3] workqueue: move rebind_hold to idle_rebind Lai Jiangshan
2012-08-29 16:51 ` [PATCH 6/9 V3] workqueue: simple clear WORKER_REBIND Lai Jiangshan
2012-08-29 16:51 ` [PATCH 7/9 V3] workqueue: explicit way to wait for idles workers to finish Lai Jiangshan
2012-08-29 18:34 ` Tejun Heo
2012-08-29 16:51 ` [PATCH 8/9 V3] workqueue: single pass rebind_workers Lai Jiangshan
2012-08-29 18:40 ` Tejun Heo
2012-08-29 16:52 ` [PATCH 9/9 V3] workqueue: merge the role of rebind_hold to idle_done Lai Jiangshan
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