[PATCH] regulator: core: regulator_lock_two() should test for EDEADLK not EDEADLOCK

[PATCH] regulator: core: regulator_lock_two() should test for EDEADLK not EDEADLOCK

[Timur Tabi]

Compare against -EDEADLK, which is what ww_mutex_lock() actually
returns and what every other deadlock check in this file already uses.

Function regulator_lock_two() acquires two regulators via
regulator_lock_nested() -> ww_mutex_lock().  On contention,
ww_mutex_lock() returns -EDEADLK, which is the caller's signal to drop
the lock it holds and retry the acquisition in the canonical order.

However, regulator_lock_two() tests the return value against -EDEADLOCK
rather than -EDEADLK.  On most architectures, EDEADLK and EDEADLOCK are
the same value, so the comparison happens to be correct and the bug is
invisible.  But on MIPS, SPARC, and PowerPC, those two errors have
different values.  The test is wrong: a genuine -EDEADLK backoff no
longer matches -EDEADLOCK, so instead of unlocking and retrying, the
code falls into WARN_ON(ret) and returns with only one of the two
regulators locked.

In practice, this is a bug only on MIPS, because the regulator core is
not built or used on the other two platforms.

In general, EDEADLK is preferred over EDEADLOCK for new code.

Fixes: cba6cfdc7c3f ("regulator: core: Avoid lockdep reports when resolving supplies")
Signed-off-by: Timur Tabi <ttabi@nvidia.com>
---
 drivers/regulator/core.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/regulator/core.c b/drivers/regulator/core.c
index dc5d67767336..1797929dfe56 100644
--- a/drivers/regulator/core.c
+++ b/drivers/regulator/core.c
@@ -248,7 +248,7 @@ static void regulator_lock_two(struct regulator_dev *rdev1,
 	ret = regulator_lock_nested(rdev1, ww_ctx);
 	WARN_ON(ret);
 	ret = regulator_lock_nested(rdev2, ww_ctx);
-	if (ret != -EDEADLOCK) {
+	if (ret != -EDEADLK) {
 		WARN_ON(ret);
 		goto exit;
 	}
@@ -264,7 +264,7 @@ static void regulator_lock_two(struct regulator_dev *rdev1,
 		swap(held, contended);
 		ret = regulator_lock_nested(contended, ww_ctx);
 
-		if (ret != -EDEADLOCK) {
+		if (ret != -EDEADLK) {
 			WARN_ON(ret);
 			break;
 		}
-- 
2.54.0

Re: [PATCH] regulator: core: regulator_lock_two() should test for EDEADLK not EDEADLOCK

[Mark Brown]

On Wed, 08 Jul 2026 18:57:22 -0500, Timur Tabi wrote:
> regulator: core: regulator_lock_two() should test for EDEADLK not EDEADLOCK

Applied to

   https://git.kernel.org/pub/scm/linux/kernel/git/broonie/regulator.git for-7.2

Thanks!

[1/1] regulator: core: regulator_lock_two() should test for EDEADLK not EDEADLOCK
      https://git.kernel.org/broonie/regulator/c/d38f8bd771c4

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

Re: [PATCH] regulator: core: regulator_lock_two() should test for EDEADLK not EDEADLOCK

[Doug Anderson]

Hi,

On Wed, Jul 8, 2026 at 4:58 PM Timur Tabi <ttabi@nvidia.com> wrote:
>
> Compare against -EDEADLK, which is what ww_mutex_lock() actually
> returns and what every other deadlock check in this file already uses.
>
> Function regulator_lock_two() acquires two regulators via
> regulator_lock_nested() -> ww_mutex_lock().  On contention,
> ww_mutex_lock() returns -EDEADLK, which is the caller's signal to drop
> the lock it holds and retry the acquisition in the canonical order.
>
> However, regulator_lock_two() tests the return value against -EDEADLOCK
> rather than -EDEADLK.  On most architectures, EDEADLK and EDEADLOCK are
> the same value, so the comparison happens to be correct and the bug is
> invisible.  But on MIPS, SPARC, and PowerPC, those two errors have
> different values.  The test is wrong: a genuine -EDEADLK backoff no
> longer matches -EDEADLOCK, so instead of unlocking and retrying, the
> code falls into WARN_ON(ret) and returns with only one of the two
> regulators locked.
>
> In practice, this is a bug only on MIPS, because the regulator core is
> not built or used on the other two platforms.
>
> In general, EDEADLK is preferred over EDEADLOCK for new code.
>
> Fixes: cba6cfdc7c3f ("regulator: core: Avoid lockdep reports when resolving supplies")
> Signed-off-by: Timur Tabi <ttabi@nvidia.com>
> ---
>  drivers/regulator/core.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)

Well, crud. Thanks for the fix.

Reviewed-by: Douglas Anderson <dianders@chromium.org>