Linux-rt-users archive on lore.kernel.org
 help / color / Atom feed
From: Petr Mladek <pmladek@suse.com>
To: Grygorii Strashko <grygorii.strashko@ti.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	linux-rt-users@vger.kernel.org,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	netdev <netdev@vger.kernel.org>,
	Richard Cochran <richardcochran@gmail.com>
Subject: Re: Question about kthread_mod_delayed_work() allowed context
Date: Wed, 12 Feb 2020 16:41:16 +0100
Message-ID: <20200212154116.hh2vdyi7e2xflxr5@pathway.suse.cz> (raw)
In-Reply-To: <cfa886ad-e3b7-c0d2-3ff8-58d94170eab5@ti.com>

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

  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 [this message]
2020-02-12 19:17   ` Grygorii Strashko
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:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

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

  git send-email \
    --in-reply-to=20200212154116.hh2vdyi7e2xflxr5@pathway.suse.cz \
    --to=pmladek@suse.com \
    --cc=grygorii.strashko@ti.com \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-rt-users@vger.kernel.org \
    --cc=netdev@vger.kernel.org \
    --cc=richardcochran@gmail.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

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

Linux-rt-users archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-rt-users/0 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/ https://lore.kernel.org/linux-rt-users \
		linux-rt-users@vger.kernel.org
	public-inbox-index linux-rt-users

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-rt-users


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git