drm/i915: Lock the gem_context->active_list while dropping the link

On unpinning the intel_context, we remove it from the active list
inside the GEM context. This list is supposed to be guarded by the GEM
context mutex, so remember to take it!

Fixes: 7e3d9a59 ("drm/i915: Track active engines within a context")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190318212347.30146-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/intel_context.c

@@ -165,13 +165,13 @@ intel_context_pin(struct i915_gem_context *ctx,
 		if (err)
 			goto err;
 
+		i915_gem_context_get(ctx);
+		GEM_BUG_ON(ce->gem_context != ctx);
+
 		mutex_lock(&ctx->mutex);
 		list_add(&ce->active_link, &ctx->active_engines);
 		mutex_unlock(&ctx->mutex);
 
-		i915_gem_context_get(ctx);
-		GEM_BUG_ON(ce->gem_context != ctx);
-
 		smp_mb__before_atomic(); /* flush pin before it is visible */
 	}
 
@@ -194,9 +194,16 @@ void intel_context_unpin(struct intel_context *ce)
 	/* We may be called from inside intel_context_pin() to evict another */
 	mutex_lock_nested(&ce->pin_mutex, SINGLE_DEPTH_NESTING);
 
-	if (likely(atomic_dec_and_test(&ce->pin_count)))
+	if (likely(atomic_dec_and_test(&ce->pin_count))) {
 		ce->ops->unpin(ce);
 
+		mutex_lock(&ce->gem_context->mutex);
+		list_del(&ce->active_link);
+		mutex_unlock(&ce->gem_context->mutex);
+
+		i915_gem_context_put(ce->gem_context);
+	}
+
 	mutex_unlock(&ce->pin_mutex);
 }
 

drivers/gpu/drm/i915/intel_lrc.c

@@ -1277,9 +1277,6 @@ static void execlists_context_unpin(struct intel_context *ce)
 	ce->state->obj->pin_global--;
 	i915_gem_object_unpin_map(ce->state->obj);
 	i915_vma_unpin(ce->state);
-
-	list_del(&ce->active_link);
-	i915_gem_context_put(ce->gem_context);
 }
 
 static int __context_pin(struct i915_vma *vma)

drivers/gpu/drm/i915/intel_ringbuffer.c

@@ -1430,9 +1430,6 @@ static void ring_context_unpin(struct intel_context *ce)
 {
 	__context_unpin_ppgtt(ce->gem_context);
 	__context_unpin(ce);
-
-	list_del(&ce->active_link);
-	i915_gem_context_put(ce->gem_context);
 }
 
 static struct i915_vma *

drivers/gpu/drm/i915/selftests/mock_engine.c

@@ -126,8 +126,6 @@ static void hw_delay_complete(struct timer_list *t)
 static void mock_context_unpin(struct intel_context *ce)
 {
 	mock_timeline_unpin(ce->ring->timeline);
-	list_del(&ce->active_link);
-	i915_gem_context_put(ce->gem_context);
 }
 
 static void mock_context_destroy(struct intel_context *ce)