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Date:   Thu, 27 Oct 2022 18:01:21 +0200
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From:   Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To:     "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc:     Steven Rostedt <rostedt@goodmis.org>, linux-kernel@vger.kernel.org,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Stephen Boyd <sboyd@kernel.org>,
        Guenter Roeck <linux@roeck-us.net>,
        Sultan Alsawaf <sultan@kerneltoast.com>
Subject: Re: [RFC][PATCH v2 00/31] timers: Use del_timer_shutdown() before
 freeing timers
Message-ID: <Y1qrUXkrZT1CyacK@linutronix.de>
References: <20221027150525.753064657@goodmis.org>
 <Y1qpNZuoIyvT5Edj@zx2c4.com>
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On 2022-10-27 17:52:21 [+0200], Jason A. Donenfeld wrote:
> On Thu, Oct 27, 2022 at 11:05:25AM -0400, Steven Rostedt wrote:
=E2=80=A6
>=20
> FYI, there's a related issue with add_timer_on(), currently without a
> straight forward solution, in case you're curious, discussed with
> Sebastian and Sultan a few weeks ago. Pasting from that thread, the
> issue is:
=E2=80=A6
=E2=80=A6
>=20
> It would be interesting if your patch fixed this case too. But maybe the
> above is unfixable (and rather niche anyway).

Haven't read the thread, yet, but the issue we talked about a few weeks
ago is unfixable. I plan to document this.
Eitherway CONFIG_DEBUG_OBJECTS_TIMERS should warn you here.

There are watchdogs (clocksource_watchdog()) which rotate CPUs and
invoke add_timer_on() from within the callback. This complicates
things.

> Jason

Sebastian