Messages in this thread Patch in this message | | | From | Charles Keepax <> | Subject | [PATCH] regulator: core: Avoid potential deadlock on regulator_unregister | Date | Thu, 4 Apr 2019 16:32:18 +0100 |
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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@opensource.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.
Thanks, Charles
[1] https://lore.kernel.org/lkml/20190403135531.GB81578@ediswmail.ad.cirrus.com/
drivers/regulator/core.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/drivers/regulator/core.c b/drivers/regulator/core.c index 38442eebddfc5..186a37675b50b 100644 --- a/drivers/regulator/core.c +++ b/drivers/regulator/core.c @@ -5059,10 +5059,11 @@ void regulator_unregister(struct regulator_dev *rdev) regulator_put(rdev->supply); } + flush_work(&rdev->disable_work.work); + mutex_lock(®ulator_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); -- 2.11.0
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