drm/i915: Pull sync_scru for device reset outside of wedge_mutex

We need to flush our srcu protecting resources about to be clobbered
by the reset, inside of our timer failsafe but outside of the
error->wedge_mutex, so that the failsafe can run in case the
synchronize_srcu() takes too long (hits a shrinker deadlock?).

Fixes: 72eb16df ("drm/i915: Serialise resets with wedging")
References: https://bugs.freedesktop.org/show_bug.cgi?id=109605Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190211135040.1234-1-chris@chris-wilson.co.ukReviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>

drivers/gpu/drm/i915/i915_reset.c

@@ -941,9 +941,6 @@ static int do_reset(struct drm_i915_private *i915, unsigned int stalled_mask)
 {
 	int err, i;
 
-	/* Flush everyone currently using a resource about to be clobbered */
-	synchronize_srcu(&i915->gpu_error.reset_backoff_srcu);
-
 	err = intel_gpu_reset(i915, ALL_ENGINES);
 	for (i = 0; err && i < RESET_MAX_RETRIES; i++) {
 		msleep(10 * (i + 1));
@@ -1140,6 +1137,9 @@ static void i915_reset_device(struct drm_i915_private *i915,
 	i915_wedge_on_timeout(&w, i915, 5 * HZ) {
 		intel_prepare_reset(i915);
 
+		/* Flush everyone using a resource about to be clobbered */
+		synchronize_srcu(&error->reset_backoff_srcu);
+
 		mutex_lock(&error->wedge_mutex);
 		i915_reset(i915, engine_mask, reason);
 		mutex_unlock(&error->wedge_mutex);