drm/i915/gt: Convert timeline tracking to spinlock

Convert the active_list manipulation of timelines to use spinlocks so
that we can perform the updates from underneath a quick interrupt
callback, if need be.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190815205709.24285-2-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/gt/intel_gt_types.h

@@ -40,7 +40,7 @@ struct intel_gt {
 	struct intel_uc uc;
 
 	struct intel_gt_timelines {
-		struct mutex mutex; /* protects list */
+		spinlock_t lock; /* protects active_list */
 		struct list_head active_list;
 
 		/* Pack multiple timelines' seqnos into the same page */

drivers/gpu/drm/i915/gt/intel_reset.c

@@ -811,14 +811,16 @@ static bool __intel_gt_unset_wedged(struct intel_gt *gt)
 	 *
 	 * No more can be submitted until we reset the wedged bit.
 	 */
-	mutex_lock(&timelines->mutex);
+	spin_lock(&timelines->lock);
 	list_for_each_entry(tl, &timelines->active_list, link) {
 		struct i915_request *rq;
 
 		rq = i915_active_request_get_unlocked(&tl->last_request);
 		if (!rq)
 			continue;
 
+		spin_unlock(&timelines->lock);
+
 		/*
 		 * All internal dependencies (i915_requests) will have
 		 * been flushed by the set-wedge, but we may be stuck waiting
@@ -828,8 +830,12 @@ static bool __intel_gt_unset_wedged(struct intel_gt *gt)
 		 */
 		dma_fence_default_wait(&rq->fence, false, MAX_SCHEDULE_TIMEOUT);
 		i915_request_put(rq);
+
+		/* Restart iteration after droping lock */
+		spin_lock(&timelines->lock);
+		tl = list_entry(&timelines->active_list, typeof(*tl), link);
 	}
-	mutex_unlock(&timelines->mutex);
+	spin_unlock(&timelines->lock);
 
 	intel_gt_sanitize(gt, false);
 

drivers/gpu/drm/i915/gt/intel_timeline.c

@@ -266,7 +266,7 @@ static void timelines_init(struct intel_gt *gt)
 {
 	struct intel_gt_timelines *timelines = &gt->timelines;
 
-	mutex_init(&timelines->mutex);
+	spin_lock_init(&timelines->lock);
 	INIT_LIST_HEAD(&timelines->active_list);
 
 	spin_lock_init(&timelines->hwsp_lock);
@@ -345,9 +345,9 @@ void intel_timeline_enter(struct intel_timeline *tl)
 		return;
 	GEM_BUG_ON(!tl->active_count); /* overflow? */
 
-	mutex_lock(&timelines->mutex);
+	spin_lock(&timelines->lock);
 	list_add(&tl->link, &timelines->active_list);
-	mutex_unlock(&timelines->mutex);
+	spin_unlock(&timelines->lock);
 }
 
 void intel_timeline_exit(struct intel_timeline *tl)
@@ -358,9 +358,9 @@ void intel_timeline_exit(struct intel_timeline *tl)
 	if (--tl->active_count)
 		return;
 
-	mutex_lock(&timelines->mutex);
+	spin_lock(&timelines->lock);
 	list_del(&tl->link);
-	mutex_unlock(&timelines->mutex);
+	spin_unlock(&timelines->lock);
 
 	/*
 	 * Since this timeline is idle, all bariers upon which we were waiting
@@ -548,8 +548,6 @@ static void timelines_fini(struct intel_gt *gt)
 
 	GEM_BUG_ON(!list_empty(&timelines->active_list));
 	GEM_BUG_ON(!list_empty(&timelines->hwsp_free_list));
-
-	mutex_destroy(&timelines->mutex);
 }
 
 void intel_timelines_fini(struct drm_i915_private *i915)

drivers/gpu/drm/i915/i915_gem.c

@@ -897,18 +897,18 @@ static long
 wait_for_timelines(struct drm_i915_private *i915,
 		   unsigned int flags, long timeout)
 {
-	struct intel_gt_timelines *gt = &i915->gt.timelines;
+	struct intel_gt_timelines *timelines = &i915->gt.timelines;
 	struct intel_timeline *tl;
 
-	mutex_lock(&gt->mutex);
-	list_for_each_entry(tl, &gt->active_list, link) {
+	spin_lock(&timelines->lock);
+	list_for_each_entry(tl, &timelines->active_list, link) {
 		struct i915_request *rq;
 
 		rq = i915_active_request_get_unlocked(&tl->last_request);
 		if (!rq)
 			continue;
 
-		mutex_unlock(&gt->mutex);
+		spin_unlock(&timelines->lock);
 
 		/*
 		 * "Race-to-idle".
@@ -928,10 +928,10 @@ wait_for_timelines(struct drm_i915_private *i915,
 			return timeout;
 
 		/* restart after reacquiring the lock */
-		mutex_lock(&gt->mutex);
-		tl = list_entry(&gt->active_list, typeof(*tl), link);
+		spin_lock(&timelines->lock);
+		tl = list_entry(&timelines->active_list, typeof(*tl), link);
 	}
-	mutex_unlock(&gt->mutex);
+	spin_unlock(&timelines->lock);
 
 	return timeout;
 }