linux-kernel - [PATCH] regulator: Fix lockdep warning resolving supplies

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Date:   Fri, 22 Jan 2021 13:20:42 +0000
From:   Mark Brown <broonie@...nel.org>
To:     Liam Girdwood <lgirdwood@...il.com>
Cc:     linux-kernel@...r.kernel.org, Mark Brown <broonie@...nel.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>
Subject: [PATCH] regulator: Fix lockdep warning resolving supplies

With commit eaa7995c529b54 (regulator: core: avoid
regulator_resolve_supply() race condition) we started holding the rdev
lock while resolving supplies, an operation that requires holding the
regulator_list_mutex. This results in lockdep warnings since in other
places we take the list mutex then the mutex on an individual rdev.

Since the goal is to make sure that we don't call set_supply() twice
rather than a concern about the cost of resolution pull the rdev lock
and check for duplicate resolution down to immediately before we do the
set_supply() and drop it again once the allocation is done.

Fixes: eaa7995c529b54 (regulator: core: avoid regulator_resolve_supply() race condition)
Reported-by: Marek Szyprowski <m.szyprowski@...sung.com>
Tested-by: Marek Szyprowski <m.szyprowski@...sung.com>
Signed-off-by: Mark Brown <broonie@...nel.org>
---
 drivers/regulator/core.c | 29 +++++++++++++++++------------
 1 file changed, 17 insertions(+), 12 deletions(-)

diff --git a/drivers/regulator/core.c b/drivers/regulator/core.c
index 3ae5ccd9277d..3b73634d50ff 100644
--- a/drivers/regulator/core.c
+++ b/drivers/regulator/core.c
@@ -1823,17 +1823,6 @@ static int regulator_resolve_supply(struct regulator_dev *rdev)
 	if (rdev->supply)
 		return 0;
 
-	/*
-	 * Recheck rdev->supply with rdev->mutex lock held to avoid a race
-	 * between rdev->supply null check and setting rdev->supply in
-	 * set_supply() from concurrent tasks.
-	 */
-	regulator_lock(rdev);
-
-	/* Supply just resolved by a concurrent task? */
-	if (rdev->supply)
-		goto out;
-
 	r = regulator_dev_lookup(dev, rdev->supply_name);
 	if (IS_ERR(r)) {
 		ret = PTR_ERR(r);
@@ -1885,12 +1874,29 @@ static int regulator_resolve_supply(struct regulator_dev *rdev)
 		goto out;
 	}
 
+	/*
+	 * Recheck rdev->supply with rdev->mutex lock held to avoid a race
+	 * between rdev->supply null check and setting rdev->supply in
+	 * set_supply() from concurrent tasks.
+	 */
+	regulator_lock(rdev);
+
+	/* Supply just resolved by a concurrent task? */
+	if (rdev->supply) {
+		regulator_unlock(rdev);
+		put_device(&r->dev);
+		goto out;
+	}
+
 	ret = set_supply(rdev, r);
 	if (ret < 0) {
+		regulator_unlock(rdev);
 		put_device(&r->dev);
 		goto out;
 	}
 
+	regulator_unlock(rdev);
+
 	/*
 	 * In set_machine_constraints() we may have turned this regulator on
 	 * but we couldn't propagate to the supply if it hadn't been resolved
@@ -1906,7 +1912,6 @@ static int regulator_resolve_supply(struct regulator_dev *rdev)
 	}
 
 out:
-	regulator_unlock(rdev);
 	return ret;
 }
 
-- 
2.20.1