Messages in this thread | | | Date | Mon, 14 Jul 2014 23:42:53 +0200 (CEST) | From | Thomas Gleixner <> | Subject | Re: [PATCH 1/1 V2] workqueue: remove the del_timer_sync()s in maybe_create_worker() |
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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.
Thanks,
tglx
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