Re: [PATCH 1/1 V2] workqueue: remove the del_timer_sync()s in maybe_create_worker()
From: Thomas Gleixner
Date: Mon Jul 14 2014 - 17:43:04 EST
On Tue, 15 Jul 2014, Lai Jiangshan wrote:
> On 07/14/2014 11:33 PM, Thomas Gleixner wrote:
> > On Mon, 14 Jul 2014, Tejun Heo wrote:
> >> 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?
> > Yes.
> The comments of the del_timer_sync() needs to be updated
> if I did not misunderstood?
> > If the timer callback is running on the other cpu, then it waits
> > for the callback to finish before checking whether the timer is
> > enqueued or not.
> The syncer may be interrupted here, after it comes back, the timer
> may be running again (and maybe again and again).
No. The del_timer_sync() code holds the base lock with interrupts
disabled. So it can't be interrupted.
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