regulator: Fix recursive mutex lockdep warning

A recursive lockdep warning occurs if you call
regulator_set_optimum_mode() on a regulator with a supply because
there is no nesting annotation for the rdev->mutex. To avoid this
warning, get the supply's load before locking the regulator's
mutex to avoid grabbing the same class of lock twice.

=============================================
[ INFO: possible recursive locking detected ]
3.4.0 #3257 Tainted: G        W
---------------------------------------------
swapper/0/1 is trying to acquire lock:
 (&rdev->mutex){+.+.+.}, at: [<c036e9e0>] regulator_get_voltage+0x18/0x38

but task is already holding lock:
 (&rdev->mutex){+.+.+.}, at: [<c036ef38>] regulator_set_optimum_mode+0x24/0x224

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(&rdev->mutex);
  lock(&rdev->mutex);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

3 locks held by swapper/0/1:
 #0:  (&__lockdep_no_validate__){......}, at: [<c03dbb48>] __driver_attach+0x40/0x8c
 #1:  (&__lockdep_no_validate__){......}, at: [<c03dbb58>] __driver_attach+0x50/0x8c
 #2:  (&rdev->mutex){+.+.+.}, at: [<c036ef38>] regulator_set_optimum_mode+0x24/0x224

stack backtrace:
[<c001521c>] (unwind_backtrace+0x0/0x12c) from [<c00cc4d4>] (validate_chain+0x760/0x1080)
[<c00cc4d4>] (validate_chain+0x760/0x1080) from [<c00cd744>] (__lock_acquire+0x950/0xa10)
[<c00cd744>] (__lock_acquire+0x950/0xa10) from [<c00cd990>] (lock_acquire+0x18c/0x1e8)
[<c00cd990>] (lock_acquire+0x18c/0x1e8) from [<c080c248>] (mutex_lock_nested+0x68/0x3c4)
[<c080c248>] (mutex_lock_nested+0x68/0x3c4) from [<c036e9e0>] (regulator_get_voltage+0x18/0x38)
[<c036e9e0>] (regulator_get_voltage+0x18/0x38) from [<c036efb8>] (regulator_set_optimum_mode+0xa4/0x224)
...

Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

diff --git a/drivers/regulator/core.c b/drivers/regulator/core.c
index 09a737c868b573227d22226926a081f35a29e6b2..8b4b3829d9e719f1acb57ef0d5b158beeefe914d 100644 (file)
--- a/drivers/regulator/core.c
+++ b/drivers/regulator/core.c
@@ -2519,9 +2519,12 @@ int regulator_set_optimum_mode(struct regulator *regulator, int uA_load)
 {
        struct regulator_dev *rdev = regulator->rdev;
        struct regulator *consumer;
-       int ret, output_uV, input_uV, total_uA_load = 0;
+       int ret, output_uV, input_uV = 0, total_uA_load = 0;
        unsigned int mode;
 
+       if (rdev->supply)
+               input_uV = regulator_get_voltage(rdev->supply);
+
        mutex_lock(&rdev->mutex);
 
        /*
@@ -2554,10 +2557,7 @@ int regulator_set_optimum_mode(struct regulator *regulator, int uA_load)
                goto out;
        }
 
-       /* get input voltage */
-       input_uV = 0;
-       if (rdev->supply)
-               input_uV = regulator_get_voltage(rdev->supply);
+       /* No supply? Use constraint voltage */
        if (input_uV <= 0)
                input_uV = rdev->constraints->input_uV;
        if (input_uV <= 0) {