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regulator: core: Avoid potential deadlock on regulator_unregister 

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: f8702f9e4a ("regulator: core: Use ww_mutex for regulators locking")
Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Reviewed-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
hifive-unleashed-5.2
Charles Keepax 2019-04-04 16:32:18 +01:00 committed by Mark Brown
parent 0b5e200cc7
commit 063773011d
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GPG Key ID: 24D68B725D5487D0
1 changed files with 2 additions and 1 deletions
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drivers/regulator/core.c
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@ -5061,10 +5061,11 @@ void regulator_unregister(struct regulator_dev *rdev)
regulator_put(rdev->supply);
}
flush_work(&rdev->disable_work.work);
mutex_lock(&regulator_list_mutex);
debugfs_remove_recursive(rdev->debugfs);
flush_work(&rdev->disable_work.work);
WARN_ON(rdev->open_count);
regulator_remove_coupling(rdev);
unset_regulator_supplies(rdev);