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Date:   Mon, 18 Jan 2021 20:49:58 +0000
From:   Mark Brown <broonie@kernel.org>
To:     Marek Szyprowski <m.szyprowski@samsung.com>
Cc:     David Collins <collinsd@codeaurora.org>,
        Liam Girdwood <lgirdwood@gmail.com>,
        Krzysztof Kozlowski <krzk@kernel.org>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>,
        linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org,
        'Linux Samsung SOC' <linux-samsung-soc@vger.kernel.org>
Subject: Re: [PATCH] regulator: core: avoid regulator_resolve_supply() race
 condition
Message-ID: <20210118204958.GS4455@sirena.org.uk>
References: <1610068562-4410-1-git-send-email-collinsd@codeaurora.org>
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On Tue, Jan 12, 2021 at 10:34:19PM +0100, Marek Szyprowski wrote:

> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D
> WARNING: possible circular locking dependency detected
> 5.11.0-rc1-00008-geaa7995c529b #10095 Not tainted
> ------------------------------------------------------
> swapper/0/1 is trying to acquire lock:
> c12e1b80 (regulator_list_mutex){+.+.}-{3:3}, at:=20
> regulator_lock_dependent+0x4c/0x2b0

If you're sending backtraces or other enormous reports like this please
run them through addr2line first so that things are a bit more leigible.

> but task is already holding lock:
> df7190c0 (regulator_ww_class_mutex){+.+.}-{3:3}, at:=20
> regulator_resolve_supply+0x44/0x318
>=20
> which lock already depends on the new lock.

Does this help (completely untested):

diff --git a/drivers/regulator/core.c b/drivers/regulator/core.c
index 3ae5ccd9277d..7d1422b00974 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;
=20
-	/*
-	 * 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 =3D regulator_dev_lookup(dev, rdev->supply_name);
 	if (IS_ERR(r)) {
 		ret =3D PTR_ERR(r);
@@ -1885,10 +1874,23 @@ static int regulator_resolve_supply(struct regulato=
r_dev *rdev)
 		goto out;
 	}
=20
+	/*
+	 * 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) {
+		put_device(&r->dev);
+		goto out_rdev_lock;
+	}
+
 	ret =3D set_supply(rdev, r);
 	if (ret < 0) {
 		put_device(&r->dev);
-		goto out;
+		goto out_rdev_lock;
 	}
=20
 	/*
@@ -1901,12 +1903,13 @@ static int regulator_resolve_supply(struct regulato=
r_dev *rdev)
 		if (ret < 0) {
 			_regulator_put(rdev->supply);
 			rdev->supply =3D NULL;
-			goto out;
+			goto out_rdev_lock;
 		}
 	}
=20
-out:
+out_rdev_lock:
 	regulator_unlock(rdev);
+out:
 	return ret;
 }
=20

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