Linux-rt-users archive on
 help / color / Atom feed
From: Grygorii Strashko <>
To: Petr Mladek <>
Cc: "" <>,
	Linux ARM <>,
	netdev <>,
	Richard Cochran <>
Subject: Re: Question about kthread_mod_delayed_work() allowed context
Date: Wed, 12 Feb 2020 21:17:53 +0200
Message-ID: <> (raw)
In-Reply-To: <>

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
> 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,

  reply index

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-11 10:23 Grygorii Strashko
2020-02-12 15:41 ` Petr Mladek
2020-02-12 19:17   ` Grygorii Strashko [this message]
2020-02-13  8:33     ` Petr Mladek

Reply instructions:

You may reply publically to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \ \ \ \ \ \ \ \ \

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-rt-users archive on

Archives are clonable:
	git clone --mirror linux-rt-users/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-rt-users linux-rt-users/ \
	public-inbox-index linux-rt-users

Example config snippet for mirrors

Newsgroup available over NNTP:

AGPL code for this site: git clone