drm/nouveau/pm/fan: drop the fan lock in fan_update() before rescheduling

This should fix a deadlock that has been reported to us where fan_update()
would hold the fan lock and try to grab the alarm_program_lock to reschedule
an update. On an other CPU, the alarm_program_lock would have been taken
before calling fan_update(), leading to a deadlock.

We should Cc: <stable@vger.kernel.org> # 3.9+

Reported-by: Marcin Slusarz <marcin.slusarz@gmail.com>
Tested-by: Timothée Ravier <tim@siosm.fr>
Tested-by: Boris Fersing (IRC nick fersingb, no public email address)
Signed-off-by: Martin Peres <martin.peres@free.fr>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

1 files changed, 13 insertions, 6 deletions

diff --git a/drivers/gpu/drm/nouveau/core/subdev/therm/fan.c b/drivers/gpu/drm/nouveau/core/subdev/therm/fan.c
index 95f6129eeede..29d4c417a5b3 100644
--- a/drivers/gpu/drm/nouveau/core/subdev/therm/fan.c
+++ b/drivers/gpu/drm/nouveau/core/subdev/therm/fan.c
@@ -54,8 +54,10 @@ nouveau_fan_update(struct nouveau_fan *fan, bool immediate, int target)
 
         /* check that we're not already at the target duty cycle */
         duty = fan->get(therm);
-        if (duty == target)
-                goto done;
+        if (duty == target) {
+                spin_unlock_irqrestore(&fan->lock, flags);
+                return 0;
+        }
 
         /* smooth out the fanspeed increase/decrease */
         if (!immediate && duty >= 0) {
@@ -73,8 +75,15 @@ nouveau_fan_update(struct nouveau_fan *fan, bool immediate, int target)
 
         nv_debug(therm, "FAN update: %d\n", duty);
         ret = fan->set(therm, duty);
-        if (ret)
-                goto done;
+        if (ret) {
+                spin_unlock_irqrestore(&fan->lock, flags);
+                return ret;
+        }
+
+        /* fan speed updated, drop the fan lock before grabbing the
+         * alarm-scheduling lock and risking a deadlock
+         */
+        spin_unlock_irqrestore(&fan->lock, flags);
 
         /* schedule next fan update, if not at target speed already */
         if (list_empty(&fan->alarm.head) && target != duty) {
@@ -92,8 +101,6 @@ nouveau_fan_update(struct nouveau_fan *fan, bool immediate, int target)
                 ptimer->alarm(ptimer, delay * 1000 * 1000, &fan->alarm);
         }
 
-done:
-        spin_unlock_irqrestore(&fan->lock, flags);
         return ret;
 }