Messages in this thread | | | Subject | Re: Question about kthread_mod_delayed_work() allowed context | From | Grygorii Strashko <> | Date | Wed, 12 Feb 2020 21:17:53 +0200 |
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On 12/02/2020 17:41, Petr Mladek wrote: > On Tue 2020-02-11 12:23:59, Grygorii Strashko wrote: >> Hi All, >> >> I'd like to ask question about allowed calling context for kthread_mod_delayed_work(). >> >> The comment to kthread_mod_delayed_work() says: >> >> * This function is safe to call from any context including IRQ handler. >> * See __kthread_cancel_work() and kthread_delayed_work_timer_fn() >> * for details. >> */ >> >> But it has del_timer_sync() inside which seems can't be called from hard_irq context: >> kthread_mod_delayed_work() >> |-__kthread_cancel_work() >> |- del_timer_sync() >> |- WARN_ON(in_irq() && !(timer->flags & TIMER_IRQSAFE)); > > It is safe because kthread_delayed_work_timer_fn() is IRQ safe. > Note that it uses raw_spin_lock_irqsave(). It is the reason why > the timer could have set TIMER_IRQSAFE flag, see > KTHREAD_DELAYED_WORK_INIT(). > > In more details. The timer is either canceled before the callback > is called. Or it waits for the callback but the callback is safe > because it can't sleep.
I think, my issue (warning) could be related to the fact that kthread_init_delayed_work() is used, which seems doesn't set TIMER_IRQSAFE flag.
> > >> My use case is related to PTP processing using PTP auxiliary worker: >> (commit d9535cb7b760 ("ptp: introduce ptp auxiliary worker")): >> - periodic work A is started and res-schedules itself for every dtX >> - on IRQ - the work A need to be scheduled immediately > > This is exactly where kthread_mod_delayed_work() need to be used > in the IRQ context with 0 delay. > > >> Any advice on how to proceed? >> Can kthread_queue_work() be used even if there is delayed work is >> scheduled already (in general, don't care if work A will be executed one >> more time after timer expiration)? > > Yes, it can be used this way. It should behave the same way as > the workqueue API. > > I am happy that there are more users for this API. I wanted to > convert more kthreads but it was just falling down in my TODO. > > I hope that I answered all questions. Feel free to ask more > when in doubts. > > Best Regards, > Petr >
-- Best regards, grygorii
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