[dm-devel] [dm] Planning to WARN_ON() when flush_scheduled_work() is used.

[dm-devel] [dm] Planning to WARN_ON() when flush_scheduled_work() is used.

[Tetsuo Handa]

Hello.

Like commit c4f135d64382 ("workqueue: Wrap flush_workqueue() using a macro")
says, flush_scheduled_work() is dangerous and will be forbidden. But I haven't
heard from you after https://lkml.kernel.org/r/YtF45oMcHMKXjIyy@redhat.com .

  https://lkml.kernel.org/r/49925af7-78a8-a3dd-bce6-cfc02e1a9236@I-love.SAKURA.ne.jp
  https://lkml.kernel.org/r/e170edc2-e5b9-4c8b-4ed3-7e2d7a2850dc@I-love.SAKURA.ne.jp

Please do clarify which work items does this flush_scheduled_work() need to wait.

Regards.

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Re: [dm-devel] Planning to WARN_ON() when flush_scheduled_work() is used.

[Mike Snitzer]

On Sat, Feb 11 2023 at  1:19P -0500,
Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp> wrote:

> Hello.
> 
> Like commit c4f135d64382 ("workqueue: Wrap flush_workqueue() using a macro")
> says, flush_scheduled_work() is dangerous and will be forbidden. But I haven't
> heard from you after https://lkml.kernel.org/r/YtF45oMcHMKXjIyy@redhat.com .
> 
>   https://lkml.kernel.org/r/49925af7-78a8-a3dd-bce6-cfc02e1a9236@I-love.SAKURA.ne.jp
>   https://lkml.kernel.org/r/e170edc2-e5b9-4c8b-4ed3-7e2d7a2850dc@I-love.SAKURA.ne.jp
> 
> Please do clarify which work items does this flush_scheduled_work() need to wait.
> 
> Regards.
> 

WARN_ON() seems excessive, why not WARN_ON_ONCE()?

But that aside, sorry for not looking closely and responding with
findings sooner.

BUT, I did just have a quick look at drivers/md/dm.c and its use of
flush_schduled_work(): a quick 'git blame drivers/md/dm.c' told me it
was only introduced for the benefit of DM's deferred device removal
feature (commit 2c140a246dc0b "dm: allow remove to be deferred").

Given that, I've staged these 2 commits for 6.3 inclusion:
https://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm.git/commit/?h=dm-6.3&id=68fb709113077f1f367d8a55deb01d2d6bf23b0f
https://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm.git/commit/?h=dm-6.3&id=cd4afc85b39c1b9dd63715c591829f67b07c86a8

Thanks,
Mike

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