From: Charles Keepax <ckeepax@opensource.cirrus.com>
To: <broonie@kernel.org>, <digetx@gmail.com>, <l.stach@pengutronix.de>
Cc: <lgirdwood@gmail.com>, <linux-kernel@vger.kernel.org>
Subject: Regulator Potential Deadlock
Date: Wed, 3 Apr 2019 14:55:31 +0100 [thread overview]
Message-ID: <20190403135531.GB81578@ediswmail.ad.cirrus.com> (raw)
Hi Guys,
Was testing some of my hardware and hit this potential lockup:
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);
***
DEADLOCK
***
Looks like it comes from this patch:
commit f8702f9e4aa7 ("regulator: core: Use ww_mutex for regulators locking")
The basic problem appears to be 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.
The locking appears to have got quite complex since last time I
looked at it and I am having a little difficulty working out
exactly is protecting what.
I am wondering if the flush_work can just be moved outside the
regulator_list_mutex in regulator_unregister since that mutex
doesn't seem to protect the against the work being queued anyway?
I will keep looking into this over the next couple of days,
any pointers or ideas anyone has would be greatly appreciated.
Finally, as it looks like it might take a couple of days to
figure out the locking, I am leaving on holiday on Saturday
so if you don't see a fix from my by then it might be a couple
of weeks before I can look at it again.
Thanks,
Charles
reply other threads:[~2019-04-03 13:55 UTC|newest]
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