linux-kernel - Re: [PATCH 1/1 V2] workqueue: remove the del_timer_sync()s in maybe_create

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Message-ID: <20140714142707.GB31610@htj.dyndns.org>
Date:	Mon, 14 Jul 2014 10:27:07 -0400
From:	Tejun Heo <tj@...nel.org>
To:	Lai Jiangshan <laijs@...fujitsu.com>
Cc:	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 1/1 V2] workqueue: remove the del_timer_sync()s in
 maybe_create_worker()

Hello,

On Mon, Jul 14, 2014 at 04:13:21PM +0800, Lai Jiangshan wrote:
> It is said in the document that the timer which is being
> deleted by del_timer_sync() should not be restarted:
>   Synchronization rules: Callers must prevent restarting of
>   the timer, otherwise this function is meaningless.
> 
> Repeating timer may cause the del_timer_sync() spin longer,
> or even spin forever in very very very very extreme condition.

I'm fairly sure del_timer_sync() can delete self-requeueing timers.
The implementation busy-waits if the queued timer is the currently
executing one and dequeues only while the timer isn't running which
should be able to handle self-requeueing ones just fine.  Thomas,
del_timer_sync() can reliably delete self-requeueing ones, right?

Thanks.

-- 
tejun
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