[PATCH] regulator: core: fix deadlock on regulator enable

[PATCH] regulator: core: fix deadlock on regulator enable

[Johan Hovold]

When updating the operating mode as part of regulator enable, the caller
has already locked the regulator tree and drms_uA_update() must not try
to do the same in order not to trigger a deadlock.

The lock inversion is reported by lockdep as:

  ======================================================
  WARNING: possible circular locking dependency detected
  6.1.0-next-20221215 #142 Not tainted
  ------------------------------------------------------
  udevd/154 is trying to acquire lock:
  ffffc11f123d7e50 (regulator_list_mutex){+.+.}-{3:3}, at: regulator_lock_dependent+0x54/0x280

  but task is already holding lock:
  ffff80000e4c36e8 (regulator_ww_class_acquire){+.+.}-{0:0}, at: regulator_enable+0x34/0x80

  which lock already depends on the new lock.

  ...

   Possible unsafe locking scenario:

         CPU0                    CPU1
         ----                    ----
    lock(regulator_ww_class_acquire);
                                 lock(regulator_list_mutex);
                                 lock(regulator_ww_class_acquire);
    lock(regulator_list_mutex);

   *** DEADLOCK ***

just before probe of a Qualcomm UFS controller (occasionally) deadlocks
when enabling one of its regulators.

Fixes: 9243a195be7a ("regulator: core: Change voltage setting path")
Fixes: f8702f9e4aa7 ("regulator: core: Use ww_mutex for regulators locking")
Cc: stable@vger.kernel.org      # 5.0
Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
---
 drivers/regulator/core.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/regulator/core.c b/drivers/regulator/core.c
index 729c45393803..ae69e493913d 100644
--- a/drivers/regulator/core.c
+++ b/drivers/regulator/core.c
@@ -1002,7 +1002,7 @@ static int drms_uA_update(struct regulator_dev *rdev)
 		/* get input voltage */
 		input_uV = 0;
 		if (rdev->supply)
-			input_uV = regulator_get_voltage(rdev->supply);
+			input_uV = regulator_get_voltage_rdev(rdev->supply->rdev);
 		if (input_uV <= 0)
 			input_uV = rdev->constraints->input_uV;
 
-- 
2.37.4

Re: [PATCH] regulator: core: fix deadlock on regulator enable

[Mark Brown]

On Thu, 15 Dec 2022 11:46:46 +0100, Johan Hovold wrote:
> When updating the operating mode as part of regulator enable, the caller
> has already locked the regulator tree and drms_uA_update() must not try
> to do the same in order not to trigger a deadlock.
> 
> The lock inversion is reported by lockdep as:
> 
>   ======================================================
>   WARNING: possible circular locking dependency detected
>   6.1.0-next-20221215 #142 Not tainted
>   ------------------------------------------------------
>   udevd/154 is trying to acquire lock:
>   ffffc11f123d7e50 (regulator_list_mutex){+.+.}-{3:3}, at: regulator_lock_dependent+0x54/0x280
> 
> [...]

Applied to

   https://git.kernel.org/pub/scm/linux/kernel/git/broonie/regulator.git for-next

Thanks!

[1/1] regulator: core: fix deadlock on regulator enable
      commit: cb3543cff90a4448ed560ac86c98033ad5fecda9

All being well this means that it will be integrated into the linux-next
tree (usually sometime in the next 24 hours) and sent to Linus during
the next merge window (or sooner if it is a bug fix), however if
problems are discovered then the patch may be dropped or reverted.

You may get further e-mails resulting from automated or manual testing
and review of the tree, please engage with people reporting problems and
send followup patches addressing any issues that are reported if needed.

If any updates are required or you are submitting further changes they
should be sent as incremental updates against current git, existing
patches will not be replaced.

Please add any relevant lists and maintainers to the CCs when replying
to this mail.

Thanks,
Mark