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
