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Date: Thu, 4 Apr 2019 18:55:11 +0300
From: Dmitry Osipenko <digetx@...il.com>
To: Charles Keepax <ckeepax@...nsource.cirrus.com>, broonie@...nel.org,
lgirdwood@...il.com
Cc: l.stach@...gutronix.de, linux-kernel@...r.kernel.org,
patches@...nsource.cirrus.com
Subject: Re: [PATCH] regulator: core: Avoid potential deadlock on
regulator_unregister
04.04.2019 18:32, Charles Keepax пишет:
> Lockdep reports the following issue on my setup:
>
> Possible unsafe locking scenario:
>
> CPU0 CPU1
> ---- ----
> lock((work_completion)(&(&rdev->disable_work)->work));
> lock(regulator_list_mutex);
> lock((work_completion)(&(&rdev->disable_work)->work));
> lock(regulator_list_mutex);
>
> The problem is that regulator_unregister takes the
> regulator_list_mutex and then calls flush_work on disable_work. But
> regulator_disable_work calls regulator_lock_dependent which will
> also take the regulator_list_mutex. Resulting in a deadlock if the
> flush_work call actually needs to flush the work.
>
> Fix this issue by moving the flush_work outside of the
> regulator_list_mutex. The list mutex is not used to guard the point at
> which the delayed work is queued, so its use adds no additional safety.
>
> Fixes: f8702f9e4aa7 ("regulator: core: Use ww_mutex for regulators locking")
> Signed-off-by: Charles Keepax <ckeepax@...nsource.cirrus.com>
> ---
>
> This patch follows on from my email the other day [1].
>
> After looking at things in more detail I am fairly confident this is
> a good fix. I do still have a slight nagging doubt that something
> should be protecting this flush_work from additional works being
> queued, and I can't see what that is. But as that is definitely not
> the regulator_list_mutex the patch is not making this any more
> dangerous. In practice I suspect this is fine as nothing should
> really be using a regulator that is about to be unregistered,
> or really this delayed work is probably the least of the systems
> problems.
If anything tries to use regulator after invoking the regulator_unregister(), then indeed it's already in trouble. The patch looks good to me, thanks.
Reviewed-by: Dmitry Osipenko <digetx@...il.com>
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