drm/i915: Drop the deferred active reference

An old optimisation to reduce the number of atomics per batch sadly
relies on struct_mutex for coordination. In order to remove struct_mutex
from serialising object/context closing, always taking and releasing an
active reference on first use / last use greatly simplifies the locking.
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/20190528092956.14910-15-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/gem/i915_gem_context.c

@@ -112,7 +112,7 @@ static void lut_close(struct i915_gem_context *ctx)
 		radix_tree_iter_delete(&ctx->handles_vma, &iter, slot);
 
 		vma->open_count--;
-		__i915_gem_object_release_unless_active(vma->obj);
+		i915_vma_put(vma);
 	}
 	rcu_read_unlock();
 }

drivers/gpu/drm/i915/gem/i915_gem_object.c

@@ -155,7 +155,7 @@ void i915_gem_close_object(struct drm_gem_object *gem, struct drm_file *file)
 		list_del(&lut->ctx_link);
 
 		i915_lut_handle_free(lut);
-		__i915_gem_object_release_unless_active(obj);
+		i915_gem_object_put(obj);
 	}
 
 	mutex_unlock(&i915->drm.struct_mutex);
@@ -347,17 +347,6 @@ void i915_gem_free_object(struct drm_gem_object *gem_obj)
 	call_rcu(&obj->rcu, __i915_gem_free_object_rcu);
 }
 
-void __i915_gem_object_release_unless_active(struct drm_i915_gem_object *obj)
-{
-	lockdep_assert_held(&obj->base.dev->struct_mutex);
-
-	if (!i915_gem_object_has_active_reference(obj) &&
-	    i915_gem_object_is_active(obj))
-		i915_gem_object_set_active_reference(obj);
-	else
-		i915_gem_object_put(obj);
-}
-
 static inline enum fb_op_origin
 fb_write_origin(struct drm_i915_gem_object *obj, unsigned int domain)
 {

drivers/gpu/drm/i915/gem/i915_gem_object.h

@@ -161,31 +161,9 @@ i915_gem_object_needs_async_cancel(const struct drm_i915_gem_object *obj)
 static inline bool
 i915_gem_object_is_active(const struct drm_i915_gem_object *obj)
 {
-	return obj->active_count;
+	return READ_ONCE(obj->active_count);
 }
 
-static inline bool
-i915_gem_object_has_active_reference(const struct drm_i915_gem_object *obj)
-{
-	return test_bit(I915_BO_ACTIVE_REF, &obj->flags);
-}
-
-static inline void
-i915_gem_object_set_active_reference(struct drm_i915_gem_object *obj)
-{
-	lockdep_assert_held(&obj->base.dev->struct_mutex);
-	__set_bit(I915_BO_ACTIVE_REF, &obj->flags);
-}
-
-static inline void
-i915_gem_object_clear_active_reference(struct drm_i915_gem_object *obj)
-{
-	lockdep_assert_held(&obj->base.dev->struct_mutex);
-	__clear_bit(I915_BO_ACTIVE_REF, &obj->flags);
-}
-
-void __i915_gem_object_release_unless_active(struct drm_i915_gem_object *obj);
-
 static inline bool
 i915_gem_object_is_framebuffer(const struct drm_i915_gem_object *obj)
 {

drivers/gpu/drm/i915/gem/i915_gem_object_types.h

@@ -120,14 +120,6 @@ struct drm_i915_gem_object {
 	struct list_head batch_pool_link;
 	I915_SELFTEST_DECLARE(struct list_head st_link);
 
-	unsigned long flags;
-
-	/**
-	 * Have we taken a reference for the object for incomplete GPU
-	 * activity?
-	 */
-#define I915_BO_ACTIVE_REF 0
-
 	/*
 	 * Is the object to be mapped as read-only to the GPU
 	 * Only honoured if hardware has relevant pte bit

drivers/gpu/drm/i915/gem/selftests/huge_pages.c

@@ -976,8 +976,6 @@ static int gpu_write(struct i915_vma *vma,
 	if (err)
 		goto err_request;
 
-	i915_gem_object_set_active_reference(batch->obj);
-
 	i915_vma_lock(vma);
 	err = i915_gem_object_set_to_gtt_domain(vma->obj, false);
 	if (err == 0)
@@ -996,6 +994,7 @@ static int gpu_write(struct i915_vma *vma,
 err_batch:
 	i915_vma_unpin(batch);
 	i915_vma_close(batch);
+	i915_vma_put(batch);
 
 	return err;
 }

drivers/gpu/drm/i915/gem/selftests/i915_gem_coherency.c

@@ -365,7 +365,7 @@ static int igt_gem_coherency(void *arg)
 						}
 					}
 
-					__i915_gem_object_release_unless_active(obj);
+					i915_gem_object_put(obj);
 				}
 			}
 		}
@@ -377,7 +377,7 @@ static int igt_gem_coherency(void *arg)
 	return err;
 
 put_object:
-	__i915_gem_object_release_unless_active(obj);
+	i915_gem_object_put(obj);
 	goto unlock;
 }
 

drivers/gpu/drm/i915/gem/selftests/i915_gem_context.c

@@ -318,14 +318,14 @@ static int gpu_fill(struct drm_i915_gem_object *obj,
 	if (err)
 		goto skip_request;
 
-	i915_gem_object_set_active_reference(batch->obj);
+	i915_request_add(rq);
+
 	i915_vma_unpin(batch);
 	i915_vma_close(batch);
+	i915_vma_put(batch);
 
 	i915_vma_unpin(vma);
 
-	i915_request_add(rq);
-
 	return 0;
 
 skip_request:
@@ -802,9 +802,9 @@ emit_rpcs_query(struct drm_i915_gem_object *obj,
 	if (err)
 		goto skip_request;
 
-	i915_gem_object_set_active_reference(batch->obj);
 	i915_vma_unpin(batch);
 	i915_vma_close(batch);
+	i915_vma_put(batch);
 
 	i915_vma_unpin(vma);
 
@@ -820,6 +820,7 @@ emit_rpcs_query(struct drm_i915_gem_object *obj,
 	i915_request_add(rq);
 err_batch:
 	i915_vma_unpin(batch);
+	i915_vma_put(batch);
 err_vma:
 	i915_vma_unpin(vma);
 
@@ -1365,9 +1366,9 @@ static int write_to_scratch(struct i915_gem_context *ctx,
 	if (err)
 		goto skip_request;
 
-	i915_gem_object_set_active_reference(obj);
 	i915_vma_unpin(vma);
 	i915_vma_close(vma);
+	i915_vma_put(vma);
 
 	i915_request_add(rq);
 

drivers/gpu/drm/i915/gem/selftests/i915_gem_mman.c

@@ -354,8 +354,8 @@ static int make_obj_busy(struct drm_i915_gem_object *obj)
 
 	i915_request_add(rq);
 
-	__i915_gem_object_release_unless_active(obj);
 	i915_vma_unpin(vma);
+	i915_gem_object_put(obj); /* leave it only alive via its active ref */
 
 	return err;
 }

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

@@ -527,7 +527,7 @@ static void cleanup_status_page(struct intel_engine_cs *engine)
 		i915_vma_unpin(vma);
 
 	i915_gem_object_unpin_map(vma->obj);
-	__i915_gem_object_release_unless_active(vma->obj);
+	i915_gem_object_put(vma->obj);
 }
 
 static int pin_ggtt_status_page(struct intel_engine_cs *engine,

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

@@ -1302,10 +1302,9 @@ intel_engine_create_ring(struct intel_engine_cs *engine,
 void intel_ring_free(struct kref *ref)
 {
 	struct intel_ring *ring = container_of(ref, typeof(*ring), ref);
-	struct drm_i915_gem_object *obj = ring->vma->obj;
 
 	i915_vma_close(ring->vma);
-	__i915_gem_object_release_unless_active(obj);
+	i915_vma_put(ring->vma);
 
 	i915_timeline_put(ring->timeline);
 	kfree(ring);

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

@@ -120,15 +120,8 @@ static int move_to_active(struct i915_vma *vma,
 	i915_vma_lock(vma);
 	err = i915_vma_move_to_active(vma, rq, flags);
 	i915_vma_unlock(vma);
-	if (err)
-		return err;
-
-	if (!i915_gem_object_has_active_reference(vma->obj)) {
-		i915_gem_object_get(vma->obj);
-		i915_gem_object_set_active_reference(vma->obj);
-	}
 
-	return 0;
+	return err;
 }
 
 static struct i915_request *

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

@@ -142,9 +142,6 @@ read_nonprivs(struct i915_gem_context *ctx, struct intel_engine_cs *engine)
 	}
 	intel_ring_advance(rq, cs);
 
-	i915_gem_object_get(result);
-	i915_gem_object_set_active_reference(result);
-
 	i915_request_add(rq);
 	i915_vma_unpin(vma);
 

drivers/gpu/drm/i915/gvt/scheduler.c

@@ -600,7 +600,7 @@ static void release_shadow_batch_buffer(struct intel_vgpu_workload *workload)
 				i915_vma_unpin(bb->vma);
 				i915_vma_close(bb->vma);
 			}
-			__i915_gem_object_release_unless_active(bb->obj);
+			i915_gem_object_put(bb->obj);
 		}
 		list_del(&bb->list);
 		kfree(bb);

drivers/gpu/drm/i915/i915_gem_batch_pool.c

@@ -55,7 +55,7 @@ void i915_gem_batch_pool_fini(struct i915_gem_batch_pool *pool)
 		list_for_each_entry_safe(obj, next,
 					 &pool->cache_list[n],
 					 batch_pool_link)
-			__i915_gem_object_release_unless_active(obj);
+			i915_gem_object_put(obj);
 
 		INIT_LIST_HEAD(&pool->cache_list[n]);
 	}

drivers/gpu/drm/i915/i915_gem_render_state.c

@@ -230,6 +230,6 @@ int i915_gem_render_state_emit(struct i915_request *rq)
 err_vma:
 	i915_vma_close(so.vma);
 err_obj:
-	__i915_gem_object_release_unless_active(so.obj);
+	i915_gem_object_put(so.obj);
 	return err;
 }

drivers/gpu/drm/i915/i915_vma.c

@@ -112,10 +112,7 @@ static void __i915_vma_retire(struct i915_active *ref)
 	 */
 	obj_bump_mru(obj);
 
-	if (i915_gem_object_has_active_reference(obj)) {
-		i915_gem_object_clear_active_reference(obj);
-		i915_gem_object_put(obj);
-	}
+	i915_gem_object_put(obj); /* and drop the active reference */
 }
 
 static struct i915_vma *
@@ -443,7 +440,7 @@ void i915_vma_unpin_and_release(struct i915_vma **p_vma, unsigned int flags)
 	if (flags & I915_VMA_RELEASE_MAP)
 		i915_gem_object_unpin_map(obj);
 
-	__i915_gem_object_release_unless_active(obj);
+	i915_gem_object_put(obj);
 }
 
 bool i915_vma_misplaced(const struct i915_vma *vma,
@@ -933,12 +930,12 @@ int i915_vma_move_to_active(struct i915_vma *vma,
 	 * add the active reference first and queue for it to be dropped
 	 * *last*.
 	 */
-	if (!vma->active.count)
-		obj->active_count++;
+	if (!vma->active.count && !obj->active_count++)
+		i915_gem_object_get(obj); /* once more for the active ref */
 
 	if (unlikely(i915_active_ref(&vma->active, rq->fence.context, rq))) {
-		if (!vma->active.count)
-			obj->active_count--;
+		if (!vma->active.count && !--obj->active_count)
+			i915_gem_object_put(obj);
 		return -ENOMEM;
 	}
 

drivers/gpu/drm/i915/selftests/i915_request.c

@@ -869,11 +869,6 @@ static int live_all_engines(void *arg)
 		GEM_BUG_ON(err);
 		request[id]->batch = batch;
 
-		if (!i915_gem_object_has_active_reference(batch->obj)) {
-			i915_gem_object_get(batch->obj);
-			i915_gem_object_set_active_reference(batch->obj);
-		}
-
 		i915_vma_lock(batch);
 		err = i915_vma_move_to_active(batch, request[id], 0);
 		i915_vma_unlock(batch);
@@ -996,9 +991,6 @@ static int live_sequential_engines(void *arg)
 		i915_vma_unlock(batch);
 		GEM_BUG_ON(err);
 
-		i915_gem_object_set_active_reference(batch->obj);
-		i915_vma_get(batch);
-
 		i915_request_get(request[id]);
 		i915_request_add(request[id]);
 

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

@@ -79,15 +79,8 @@ static int move_to_active(struct i915_vma *vma,
 	i915_vma_lock(vma);
 	err = i915_vma_move_to_active(vma, rq, flags);
 	i915_vma_unlock(vma);
-	if (err)
-		return err;
-
-	if (!i915_gem_object_has_active_reference(vma->obj)) {
-		i915_gem_object_get(vma->obj);
-		i915_gem_object_set_active_reference(vma->obj);
-	}
 
-	return 0;
+	return err;
 }
 
 struct i915_request *