linux-kernel - Re: [PATCH 2/3] kthread: Prevent deadlock when kthread_mod_delayed_work() races with kthread_cancel_delayed_work

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Date:   Fri, 11 Jun 2021 09:16:52 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Martin Liu <liumartin@...gle.com>, Oleg Nesterov <oleg@...hat.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tejun Heo <tj@...nel.org>, minchan@...gle.com,
        davidchao@...gle.com, jenhaochen@...gle.com,
        clang-built-linux@...glegroups.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] kthread: Prevent deadlock when
 kthread_mod_delayed_work() races with kthread_cancel_delayed_work_sync()

On Thu 2021-06-10 14:30:30, Andrew Morton wrote:
> On Thu, 10 Jun 2021 15:30:50 +0200 Petr Mladek <pmladek@...e.com> wrote:
> 
> > The system might hang with the following backtrace:
> 
> Well that's not good.

Fortunately, the API users normally synchronize these operations
another way. The race should never happen when the API is used
a reasonable way,
see https://lore.kernel.org/lkml/YKZLnTNOlUQ85F2s@alley/

> > Fixes: 9a6b06c8d9a220860468a ("kthread: allow to modify delayed kthread work")
> > Reported-by: Martin Liu <liumartin@...gle.com>
> > Signed-off-by: Petr Mladek <pmladek@...e.com>
> 
> Was a -stable backport considered?

Good point! It would make sense to backport it. System hang is never
good.

Could you please add Cc: stable@...r.kernel.org or should I resend the
patchset?

Best Regards,
Petr