linux-kernel - [PATCH 4.4 113/163] regulator: core: fix regulator_lock

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Date:	Mon,  2 May 2016 17:12:21 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Geert Uytterhoeven <geert@...ux-m68k.org>,
	Arnd Bergmann <arnd@...db.de>, Mark Brown <broonie@...nel.org>,
	Guenter Roeck <linux@...ck-us.net>
Subject: [PATCH 4.4 113/163] regulator: core: fix regulator_lock_supply regression

4.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Arnd Bergmann <arnd@...db.de>

commit bb41897e38c53458a88b271f2fbcd905ee1f9584 upstream.

As noticed by Geert Uytterhoeven, my patch to avoid a harmless build warning
in regulator_lock_supply() was total crap and introduced a real bug:

> [ BUG: bad unlock balance detected! ]
> kworker/u4:0/6 is trying to release lock (&rdev->mutex) at:
> [<c0247b84>] regulator_set_voltage+0x38/0x50

we still lock the regulator supplies, but not the actual regulators,
so we are missing a lock, and the unlock is unbalanced.

This rectifies it by first locking the regulator device itself before
using the same loop as before to lock its supplies.

Reported-by: Geert Uytterhoeven <geert@...ux-m68k.org>
Signed-off-by: Arnd Bergmann <arnd@...db.de>
Fixes: 716fec9d1965 ("[SUBMITTED] regulator: core: avoid unused variable warning")
Signed-off-by: Mark Brown <broonie@...nel.org>
Cc: Guenter Roeck <linux@...ck-us.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/regulator/core.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/regulator/core.c
+++ b/drivers/regulator/core.c
@@ -140,7 +140,8 @@ static void regulator_lock_supply(struct
 {
 	int i;
 
-	for (i = 0; rdev->supply; rdev = rdev->supply->rdev, i++)
+	mutex_lock(&rdev->mutex);
+	for (i = 1; rdev->supply; rdev = rdev->supply->rdev, i++)
 		mutex_lock_nested(&rdev->mutex, i);
 }