On 07/15/2014 05:42 AM, Thomas Gleixner wrote: > 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. >
The del_timer_sync() waits via cpu_relax() without interrupts disabled. Could you wipe out my concern? > > . > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/