drm/i915: Only call mod_timer() if not already pending

The final arrangement of updating timer->expires and calling mod_timer()
used in

commit 672e7b7c1849c904b2c55185906b3940843c55c6
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date:   Wed Nov 19 09:47:19 2014 +0000

    drm/i915: Don't continually defer the hangcheck

turns out to be very unsafe. Try again.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

1 files changed, 4 insertions, 3 deletions

diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index 8d169e152d1e..5908580d7c15 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -3067,9 +3067,10 @@ void i915_queue_hangcheck(struct drm_device *dev)
                 return;
 
         /* Don't continually defer the hangcheck, but make sure it is active */
-        if (!timer_pending(timer))
-                timer->expires = round_jiffies_up(jiffies + DRM_I915_HANGCHECK_JIFFIES);
-        mod_timer(timer, timer->expires);
+        if (timer_pending(timer))
+                return;
+        mod_timer(timer,
+                  round_jiffies_up(jiffies + DRM_I915_HANGCHECK_JIFFIES));
 }
 
 static void ibx_irq_reset(struct drm_device *dev)