Messages in this thread | | | Date | Wed, 12 Feb 2020 16:41:16 +0100 | From | Petr Mladek <> | Subject | Re: Question about kthread_mod_delayed_work() allowed context |
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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.
> 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
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