linux-kernel - Re: [RFC][PATCH 3/5] timekeeping: Avoid possible deadlock from clock_was_set

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Date:	Thu, 12 Dec 2013 11:34:58 -0500
From:	Sasha Levin <sasha.levin@...cle.com>
To:	John Stultz <john.stultz@...aro.org>,
	LKML <linux-kernel@...r.kernel.org>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	Prarit Bhargava <prarit@...hat.com>,
	Richard Cochran <richardcochran@...il.com>,
	Ingo Molnar <mingo@...nel.org>, stable <stable@...r.kernel.org>
Subject: Re: [RFC][PATCH 3/5] timekeeping: Avoid possible deadlock from clock_was_set_delayed

On 12/11/2013 02:11 PM, John Stultz wrote:
> As part of normal operaions, the hrtimer subsystem frequently calls
> into the timekeeping code, creating a locking order of
>    hrtimer locks -> timekeeping locks
>
> clock_was_set_delayed() was suppoed to allow us to avoid deadlocks
> between the timekeeping the hrtimer subsystem, so that we could
> notify the hrtimer subsytem the time had changed while holding
> the timekeeping locks. This was done by scheduling delayed work
> that would run later once we were out of the timekeeing code.
>
> But unfortunately the lock chains are complex enoguh that in
> scheduling delayed work, we end up eventually trying to grab
> an hrtimer lock.
>
> Sasha Levin noticed this in testing when the new seqlock lockdep
> enablement triggered the following (somewhat abrieviated) message:

[snip]

This seems to work for me, I don't see the lockdep spew anymore.

	Tested-by: Sasha Levin <sasha.levin@...cle.com>


Thanks,
Sasha
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