[PATCH, RESEND] regulator: core: fix regulator_lock_supply regression

[PATCH, RESEND] regulator: core: fix regulator_lock_supply regression

[Arnd Bergmann]

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@linux-m68k.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: 716fec9d1965 ("[SUBMITTED] regulator: core: avoid unused variable warning")
---
rebased on top of regulators.git #for-next

diff --git a/drivers/regulator/core.c b/drivers/regulator/core.c
index c9bdca5f3b9b..89e4dcb84758 100644
--- a/drivers/regulator/core.c
+++ b/drivers/regulator/core.c
@@ -140,7 +140,8 @@ static void regulator_lock_supply(struct regulator_dev *rdev)
 {
 	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);
 }
 

[PATCH, RESEND] regulator: core: fix regulator_lock_supply regression

[Mark Brown]

On Fri, Nov 27, 2015 at 02:46:41PM +0100, Arnd Bergmann wrote:
> 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:

I'm going to drop both this and the commit it's fixing for now as this
is causing boot failures on several boards (none of which I have sadly)
in -next:

  http://kernelci.org/boot/all/job/broonie-regulator/kernel/v4.4-rc3-17-ga6498dba8869/

which were bisected by Tyler to this:

  http://hastebin.com/noluripepa.sm

I'm not seeing anything obvious in the code at the minute having looked
for several seconds, I'll have a proper look later today all being well.
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[PATCH, RESEND] regulator: core: fix regulator_lock_supply regression

[Arnd Bergmann]

On Tuesday 01 December 2015 13:16:39 Mark Brown wrote:
> On Fri, Nov 27, 2015 at 02:46:41PM +0100, Arnd Bergmann wrote:
> > 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:
> 
> I'm going to drop both this and the commit it's fixing for now as this
> is causing boot failures on several boards (none of which I have sadly)
> in -next:
> 
>   http://kernelci.org/boot/all/job/broonie-regulator/kernel/v4.4-rc3-17-ga6498dba8869/
> 
> which were bisected by Tyler to this:
> 
>   http://hastebin.com/noluripepa.sm
> 
> I'm not seeing anything obvious in the code at the minute having looked
> for several seconds, I'll have a proper look later today all being well.
> 

Ok, sorry about the double screwup and thanks for looking into it.

	Arnd