Revert "drm/i915: Extend LRC pinning to cover GPU context writeback"

This reverts commit 6d65ba943a2d1e4292a07ca7ddb6c5138b9efa5d.

Mika Kuoppala traced down a use-after-free crash in module unload to
this commit, because ring->last_context is leaked beyond when the
context gets destroyed. Mika submitted a quick fix to patch that up in
the context destruction code, but that's too much of a hack.

The right fix is instead for the ring to hold a full reference onto
it's last context, like we do for legacy contexts.

Since this is causing a regression in BAT it gets reverted before we
can close this.

Cc: Nick Hoath <nicholas.hoath@intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: David Gordon <david.s.gordon@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Alex Dai <yu.dai@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=93248
Acked-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>

drivers/gpu/drm/i915/i915_drv.h

@@ -884,7 +884,6 @@ struct intel_context {
 	struct {
 		struct drm_i915_gem_object *state;
 		struct intel_ringbuffer *ringbuf;
-		bool dirty;
 		int pin_count;
 	} engine[I915_NUM_RINGS];
 

drivers/gpu/drm/i915/i915_gem.c

@@ -1354,9 +1354,6 @@ static void i915_gem_request_retire(struct drm_i915_gem_request *request)
 {
 	trace_i915_gem_request_retire(request);
 
-	if (i915.enable_execlists)
-		intel_lr_context_complete_check(request);
-
 	/* We know the GPU must have read the request to have
 	 * sent us the seqno + interrupt, so use the position
 	 * of tail of the request to update the last known position
@@ -2767,6 +2764,10 @@ static void i915_gem_reset_ring_cleanup(struct drm_i915_private *dev_priv,
 					struct drm_i915_gem_request,
 					execlist_link);
 			list_del(&submit_req->execlist_link);
+
+			if (submit_req->ctx != ring->default_context)
+				intel_lr_context_unpin(submit_req);
+
 			i915_gem_request_unreference(submit_req);
 		}
 		spin_unlock_irq(&ring->execlist_lock);

drivers/gpu/drm/i915/intel_lrc.c

@@ -571,6 +571,9 @@ static int execlists_context_queue(struct drm_i915_gem_request *request)
 	struct drm_i915_gem_request *cursor;
 	int num_elements = 0;
 
+	if (request->ctx != ring->default_context)
+		intel_lr_context_pin(request);
+
 	i915_gem_request_reference(request);
 
 	spin_lock_irq(&ring->execlist_lock);
@@ -734,13 +737,6 @@ intel_logical_ring_advance_and_submit(struct drm_i915_gem_request *request)
 	if (intel_ring_stopped(ring))
 		return;
 
-	if (request->ctx != ring->default_context) {
-		if (!request->ctx->engine[ring->id].dirty) {
-			intel_lr_context_pin(request);
-			request->ctx->engine[ring->id].dirty = true;
-		}
-	}
-
 	if (dev_priv->guc.execbuf_client)
 		i915_guc_submit(dev_priv->guc.execbuf_client, request);
 	else
@@ -967,6 +963,12 @@ void intel_execlists_retire_requests(struct intel_engine_cs *ring)
 	spin_unlock_irq(&ring->execlist_lock);
 
 	list_for_each_entry_safe(req, tmp, &retired_list, execlist_link) {
+		struct intel_context *ctx = req->ctx;
+		struct drm_i915_gem_object *ctx_obj =
+				ctx->engine[ring->id].state;
+
+		if (ctx_obj && (ctx != ring->default_context))
+			intel_lr_context_unpin(req);
 		list_del(&req->execlist_link);
 		i915_gem_request_unreference(req);
 	}
@@ -1061,39 +1063,21 @@ reset_pin_count:
 	return ret;
 }
 
-static void __intel_lr_context_unpin(struct intel_engine_cs *ring,
-		struct intel_context *ctx)
+void intel_lr_context_unpin(struct drm_i915_gem_request *rq)
 {
-	struct drm_i915_gem_object *ctx_obj = ctx->engine[ring->id].state;
-	struct intel_ringbuffer *ringbuf = ctx->engine[ring->id].ringbuf;
+	struct intel_engine_cs *ring = rq->ring;
+	struct drm_i915_gem_object *ctx_obj = rq->ctx->engine[ring->id].state;
+	struct intel_ringbuffer *ringbuf = rq->ringbuf;
+
 	if (ctx_obj) {
 		WARN_ON(!mutex_is_locked(&ring->dev->struct_mutex));
-		if (--ctx->engine[ring->id].pin_count == 0) {
+		if (--rq->ctx->engine[ring->id].pin_count == 0) {
 			intel_unpin_ringbuffer_obj(ringbuf);
 			i915_gem_object_ggtt_unpin(ctx_obj);
 		}
 	}
 }
 
-void intel_lr_context_unpin(struct drm_i915_gem_request *rq)
-{
-	__intel_lr_context_unpin(rq->ring, rq->ctx);
-}
-
-void intel_lr_context_complete_check(struct drm_i915_gem_request *req)
-{
-	struct intel_engine_cs *ring = req->ring;
-
-	if (ring->last_context && ring->last_context != req->ctx &&
-			ring->last_context->engine[ring->id].dirty) {
-		__intel_lr_context_unpin(
-				ring,
-				ring->last_context);
-		ring->last_context->engine[ring->id].dirty = false;
-	}
-	ring->last_context = req->ctx;
-}
-
 static int intel_logical_ring_workarounds_emit(struct drm_i915_gem_request *req)
 {
 	int ret, i;
@@ -2367,76 +2351,6 @@ populate_lr_context(struct intel_context *ctx, struct drm_i915_gem_object *ctx_o
 	return 0;
 }
 
-/**
- * intel_lr_context_clean_ring() - clean the ring specific parts of an LRC
- * @ctx: the LR context being freed.
- * @ring: the engine being cleaned
- * @ctx_obj: the hw context being unreferenced
- * @ringbuf: the ringbuf being freed
- *
- * Take care of cleaning up the per-engine backing
- * objects and the logical ringbuffer.
- */
-static void
-intel_lr_context_clean_ring(struct intel_context *ctx,
-			    struct intel_engine_cs *ring,
-			    struct drm_i915_gem_object *ctx_obj,
-			    struct intel_ringbuffer *ringbuf)
-{
-	int ret;
-
-	WARN_ON(!mutex_is_locked(&ring->dev->struct_mutex));
-
-	if (ctx == ring->default_context) {
-		intel_unpin_ringbuffer_obj(ringbuf);
-		i915_gem_object_ggtt_unpin(ctx_obj);
-	}
-
-	if (ctx->engine[ring->id].dirty) {
-		struct drm_i915_gem_request *req = NULL;
-
-		/**
-		 * If there is already a request pending on
-		 * this ring, wait for that to complete,
-		 * otherwise create a switch to idle request
-		 */
-		if (list_empty(&ring->request_list)) {
-			int ret;
-
-			ret = i915_gem_request_alloc(
-					ring,
-					ring->default_context,
-					&req);
-			if (!ret)
-				i915_add_request(req);
-			else
-				DRM_DEBUG("Failed to ensure context saved");
-		} else {
-			req = list_first_entry(
-					&ring->request_list,
-					typeof(*req), list);
-		}
-		if (req) {
-			ret = i915_wait_request(req);
-			if (ret != 0) {
-				/**
-				 * If we get here, there's probably been a ring
-				 * reset, so we just clean up the dirty flag.&
-				 * pin count.
-				 */
-				ctx->engine[ring->id].dirty = false;
-				__intel_lr_context_unpin(
-					ring,
-					ctx);
-			}
-		}
-	}
-
-	WARN_ON(ctx->engine[ring->id].pin_count);
-	intel_ringbuffer_free(ringbuf);
-	drm_gem_object_unreference(&ctx_obj->base);
-}
-
 /**
  * intel_lr_context_free() - free the LRC specific bits of a context
  * @ctx: the LR context to free.
@@ -2449,7 +2363,7 @@ void intel_lr_context_free(struct intel_context *ctx)
 {
 	int i;
 
-	for (i = 0; i < I915_NUM_RINGS; ++i) {
+	for (i = 0; i < I915_NUM_RINGS; i++) {
 		struct drm_i915_gem_object *ctx_obj = ctx->engine[i].state;
 
 		if (ctx_obj) {
@@ -2457,10 +2371,13 @@ void intel_lr_context_free(struct intel_context *ctx)
 					ctx->engine[i].ringbuf;
 			struct intel_engine_cs *ring = ringbuf->ring;
 
-			intel_lr_context_clean_ring(ctx,
-						    ring,
-						    ctx_obj,
-						    ringbuf);
+			if (ctx == ring->default_context) {
+				intel_unpin_ringbuffer_obj(ringbuf);
+				i915_gem_object_ggtt_unpin(ctx_obj);
+			}
+			WARN_ON(ctx->engine[ring->id].pin_count);
+			intel_ringbuffer_free(ringbuf);
+			drm_gem_object_unreference(&ctx_obj->base);
 		}
 	}
 }
@@ -2622,12 +2539,5 @@ void intel_lr_context_reset(struct drm_device *dev,
 
 		ringbuf->head = 0;
 		ringbuf->tail = 0;
-
-		if (ctx->engine[ring->id].dirty) {
-			__intel_lr_context_unpin(
-					ring,
-					ctx);
-			ctx->engine[ring->id].dirty = false;
-		}
 	}
 }

drivers/gpu/drm/i915/intel_lrc.h

@@ -91,7 +91,6 @@ void intel_lr_context_reset(struct drm_device *dev,
 			struct intel_context *ctx);
 uint64_t intel_lr_context_descriptor(struct intel_context *ctx,
 				     struct intel_engine_cs *ring);
-void intel_lr_context_complete_check(struct drm_i915_gem_request *req);
 
 /* Execlists */
 int intel_sanitize_enable_execlists(struct drm_device *dev, int enable_execlists);