* Question about kthread_mod_delayed_work() allowed context
@ 2020-02-11 10:23 Grygorii Strashko
2020-02-12 15:41 ` Petr Mladek
0 siblings, 1 reply; 4+ messages in thread
From: Grygorii Strashko @ 2020-02-11 10:23 UTC (permalink / raw)
To: linux-kernel, Petr Mladek
Cc: netdev, Richard Cochran, linux-rt-users, Linux ARM
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));
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
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)?
--
Best regards,
grygorii
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: Question about kthread_mod_delayed_work() allowed context
2020-02-11 10:23 Question about kthread_mod_delayed_work() allowed context Grygorii Strashko
@ 2020-02-12 15:41 ` Petr Mladek
2020-02-12 19:17 ` Grygorii Strashko
0 siblings, 1 reply; 4+ messages in thread
From: Petr Mladek @ 2020-02-12 15:41 UTC (permalink / raw)
To: Grygorii Strashko
Cc: netdev, Richard Cochran, linux-kernel, Linux ARM, linux-rt-users
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
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: Question about kthread_mod_delayed_work() allowed context
2020-02-12 15:41 ` Petr Mladek
@ 2020-02-12 19:17 ` Grygorii Strashko
2020-02-13 8:33 ` Petr Mladek
0 siblings, 1 reply; 4+ messages in thread
From: Grygorii Strashko @ 2020-02-12 19:17 UTC (permalink / raw)
To: Petr Mladek
Cc: netdev, Richard Cochran, linux-kernel, Linux ARM, linux-rt-users
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
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: Question about kthread_mod_delayed_work() allowed context
2020-02-12 19:17 ` Grygorii Strashko
@ 2020-02-13 8:33 ` Petr Mladek
0 siblings, 0 replies; 4+ messages in thread
From: Petr Mladek @ 2020-02-13 8:33 UTC (permalink / raw)
To: Grygorii Strashko
Cc: netdev, Richard Cochran, linux-kernel, Linux ARM, linux-rt-users
On Wed 2020-02-12 21:17:53, Grygorii Strashko wrote:
>
>
> 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.
Great catch!
It is a bug. Would you like to send the fix for
kthread_init_delayed_work() or would you prefer me doing so?
Best Regards,
Petr
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
^ permalink raw reply [flat|nested] 4+ messages in thread
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2020-02-11 10:23 Question about kthread_mod_delayed_work() allowed context Grygorii Strashko
2020-02-12 15:41 ` Petr Mladek
2020-02-12 19:17 ` Grygorii Strashko
2020-02-13 8:33 ` Petr Mladek
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