drm/i915: Coordinate i915_active with its own mutex

Forgo the struct_mutex serialisation for i915_active, and interpose its
own mutex handling for active/retire.

This is a multi-layered sleight-of-hand. First, we had to ensure that no
active/retire callbacks accidentally inverted the mutex ordering rules,
nor assumed that they were themselves serialised by struct_mutex. More
challenging though, is the rule over updating elements of the active
rbtree. Instead of the whole i915_active now being serialised by
struct_mutex, allocations/rotations of the tree are serialised by the
i915_active.mutex and individual nodes are serialised by the caller
using the i915_timeline.mutex (we need to use nested spinlocks to
interact with the dma_fence callback lists).

The pain point here is that instead of a single mutex around execbuf, we
now have to take a mutex for active tracker (one for each vma, context,
etc) and a couple of spinlocks for each fence update. The improvement in
fine grained locking allowing for multiple concurrent clients
(eventually!) should be worth it in typical loads.

v2: Add some comments that barely elucidate anything :(
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/20191004134015.13204-6-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/display/intel_frontbuffer.c

@@ -257,7 +257,7 @@ intel_frontbuffer_get(struct drm_i915_gem_object *obj)
 	front->obj = obj;
 	kref_init(&front->ref);
 	atomic_set(&front->bits, 0);
-	i915_active_init(i915, &front->write,
+	i915_active_init(&front->write,
 			 frontbuffer_active,
 			 i915_active_may_sleep(frontbuffer_retire));
 

drivers/gpu/drm/i915/display/intel_overlay.c

@@ -1360,8 +1360,7 @@ void intel_overlay_setup(struct drm_i915_private *dev_priv)
 	overlay->contrast = 75;
 	overlay->saturation = 146;
 
-	i915_active_init(dev_priv,
-			 &overlay->last_flip,
+	i915_active_init(&overlay->last_flip,
 			 NULL, intel_overlay_last_flip_retire);
 
 	ret = get_registers(overlay, OVERLAY_NEEDS_PHYSICAL(dev_priv));

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

@@ -868,20 +868,18 @@ static int context_barrier_task(struct i915_gem_context *ctx,
 				void (*task)(void *data),
 				void *data)
 {
-	struct drm_i915_private *i915 = ctx->i915;
 	struct context_barrier_task *cb;
 	struct i915_gem_engines_iter it;
 	struct intel_context *ce;
 	int err = 0;
 
-	lockdep_assert_held(&i915->drm.struct_mutex);
 	GEM_BUG_ON(!task);
 
 	cb = kmalloc(sizeof(*cb), GFP_KERNEL);
 	if (!cb)
 		return -ENOMEM;
 
-	i915_active_init(i915, &cb->base, NULL, cb_retire);
+	i915_active_init(&cb->base, NULL, cb_retire);
 	err = i915_active_acquire(&cb->base);
 	if (err) {
 		kfree(cb);

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

@@ -8,6 +8,7 @@
 #define __I915_GEM_OBJECT_TYPES_H__
 
 #include <drm/drm_gem.h>
+#include <uapi/drm/i915_drm.h>
 
 #include "i915_active.h"
 #include "i915_selftest.h"

drivers/gpu/drm/i915/gem/i915_gem_pm.c

@@ -16,14 +16,11 @@ static void call_idle_barriers(struct intel_engine_cs *engine)
 	struct llist_node *node, *next;
 
 	llist_for_each_safe(node, next, llist_del_all(&engine->barrier_tasks)) {
-		struct i915_active_request *active =
+		struct dma_fence_cb *cb =
 			container_of((struct list_head *)node,
-				     typeof(*active), link);
+				     typeof(*cb), node);
 
-		INIT_LIST_HEAD(&active->link);
-		RCU_INIT_POINTER(active->request, NULL);
-
-		active->retire(active, NULL);
+		cb->func(NULL, cb);
 	}
 }
 

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

@@ -240,7 +240,7 @@ intel_context_init(struct intel_context *ce,
 
 	mutex_init(&ce->pin_mutex);
 
-	i915_active_init(ctx->i915, &ce->active,
+	i915_active_init(&ce->active,
 			 __intel_context_active, __intel_context_retire);
 }
 
@@ -307,7 +307,7 @@ int intel_context_prepare_remote_request(struct intel_context *ce,
 			return err;
 
 		/* Queue this switch after current activity by this context. */
-		err = i915_active_request_set(&tl->last_request, rq);
+		err = i915_active_fence_set(&tl->last_request, rq);
 		mutex_unlock(&tl->mutex);
 		if (err)
 			return err;

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

@@ -95,7 +95,7 @@ node_create(struct intel_engine_pool *pool, size_t sz)
 		return ERR_PTR(-ENOMEM);
 
 	node->pool = pool;
-	i915_active_init(engine->i915, &node->active, pool_active, pool_retire);
+	i915_active_init(&node->active, pool_active, pool_retire);
 
 	obj = i915_gem_object_create_internal(engine->i915, sz);
 	if (IS_ERR(obj)) {

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

@@ -844,10 +844,10 @@ static bool __intel_gt_unset_wedged(struct intel_gt *gt)
 	 */
 	spin_lock_irqsave(&timelines->lock, flags);
 	list_for_each_entry(tl, &timelines->active_list, link) {
-		struct i915_request *rq;
+		struct dma_fence *fence;
 
-		rq = i915_active_request_get_unlocked(&tl->last_request);
-		if (!rq)
+		fence = i915_active_fence_get(&tl->last_request);
+		if (!fence)
 			continue;
 
 		spin_unlock_irqrestore(&timelines->lock, flags);
@@ -859,8 +859,8 @@ static bool __intel_gt_unset_wedged(struct intel_gt *gt)
 		 * (I915_FENCE_TIMEOUT) so this wait should not be unbounded
 		 * in the worst case.
 		 */
-		dma_fence_default_wait(&rq->fence, false, MAX_SCHEDULE_TIMEOUT);
-		i915_request_put(rq);
+		dma_fence_default_wait(fence, false, MAX_SCHEDULE_TIMEOUT);
+		dma_fence_put(fence);
 
 		/* Restart iteration after droping lock */
 		spin_lock_irqsave(&timelines->lock, flags);

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

@@ -178,8 +178,7 @@ cacheline_alloc(struct intel_timeline_hwsp *hwsp, unsigned int cacheline)
 	cl->hwsp = hwsp;
 	cl->vaddr = page_pack_bits(vaddr, cacheline);
 
-	i915_active_init(hwsp->gt->i915, &cl->active,
-			 __cacheline_active, __cacheline_retire);
+	i915_active_init(&cl->active, __cacheline_active, __cacheline_retire);
 
 	return cl;
 }
@@ -255,7 +254,7 @@ int intel_timeline_init(struct intel_timeline *timeline,
 
 	mutex_init(&timeline->mutex);
 
-	INIT_ACTIVE_REQUEST(&timeline->last_request, &timeline->mutex);
+	INIT_ACTIVE_FENCE(&timeline->last_request, &timeline->mutex);
 	INIT_LIST_HEAD(&timeline->requests);
 
 	i915_syncmap_init(&timeline->sync);
@@ -443,7 +442,7 @@ __intel_timeline_get_seqno(struct intel_timeline *tl,
 	 * free it after the current request is retired, which ensures that
 	 * all writes into the cacheline from previous requests are complete.
 	 */
-	err = i915_active_ref(&tl->hwsp_cacheline->active, tl, rq);
+	err = i915_active_ref(&tl->hwsp_cacheline->active, tl, &rq->fence);
 	if (err)
 		goto err_cacheline;
 

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

@@ -58,12 +58,13 @@ struct intel_timeline {
 	 */
 	struct list_head requests;
 
-	/* Contains an RCU guarded pointer to the last request. No reference is
+	/*
+	 * Contains an RCU guarded pointer to the last request. No reference is
 	 * held to the request, users must carefully acquire a reference to
-	 * the request using i915_active_request_get_request_rcu(), or hold the
-	 * struct_mutex.
+	 * the request using i915_active_fence_get(), or manage the RCU
+	 * protection themselves (cf the i915_active_fence API).
 	 */
-	struct i915_active_request last_request;
+	struct i915_active_fence last_request;
 
 	/**
 	 * We track the most recent seqno that we wait on in every context so

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

@@ -47,24 +47,20 @@ static int context_sync(struct intel_context *ce)
 
 	mutex_lock(&tl->mutex);
 	do {
-		struct i915_request *rq;
+		struct dma_fence *fence;
 		long timeout;
 
-		rcu_read_lock();
-		rq = rcu_dereference(tl->last_request.request);
-		if (rq)
-			rq = i915_request_get_rcu(rq);
-		rcu_read_unlock();
-		if (!rq)
+		fence = i915_active_fence_get(&tl->last_request);
+		if (!fence)
 			break;
 
-		timeout = i915_request_wait(rq, 0, HZ / 10);
+		timeout = dma_fence_wait_timeout(fence, false, HZ / 10);
 		if (timeout < 0)
 			err = timeout;
 		else
-			i915_request_retire_upto(rq);
+			i915_request_retire_upto(to_request(fence));
 
-		i915_request_put(rq);
+		dma_fence_put(fence);
 	} while (!err);
 	mutex_unlock(&tl->mutex);
 

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

@@ -1172,9 +1172,13 @@ static struct i915_request *dummy_request(struct intel_engine_cs *engine)
 	if (!rq)
 		return NULL;
 
-	INIT_LIST_HEAD(&rq->active_list);
 	rq->engine = engine;
 
+	spin_lock_init(&rq->lock);
+	INIT_LIST_HEAD(&rq->fence.cb_list);
+	rq->fence.lock = &rq->lock;
+	rq->fence.ops = &i915_fence_ops;
+
 	i915_sched_node_init(&rq->sched);
 
 	/* mark this request as permanently incomplete */
@@ -1267,8 +1271,8 @@ static int live_suppress_wait_preempt(void *arg)
 				}
 
 				/* Disable NEWCLIENT promotion */
-				__i915_active_request_set(&i915_request_timeline(rq[i])->last_request,
-							  dummy);
+				__i915_active_fence_set(&i915_request_timeline(rq[i])->last_request,
+							&dummy->fence);
 				i915_request_add(rq[i]);
 			}
 

drivers/gpu/drm/i915/gt/selftests/mock_timeline.c

@@ -15,7 +15,7 @@ void mock_timeline_init(struct intel_timeline *timeline, u64 context)
 
 	mutex_init(&timeline->mutex);
 
-	INIT_ACTIVE_REQUEST(&timeline->last_request, &timeline->mutex);
+	INIT_ACTIVE_FENCE(&timeline->last_request, &timeline->mutex);
 	INIT_LIST_HEAD(&timeline->requests);
 
 	i915_syncmap_init(&timeline->sync);

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

@@ -385,11 +385,8 @@ intel_gvt_workload_req_alloc(struct intel_vgpu_workload *workload)
 {
 	struct intel_vgpu *vgpu = workload->vgpu;
 	struct intel_vgpu_submission *s = &vgpu->submission;
-	struct drm_i915_private *dev_priv = vgpu->gvt->dev_priv;
 	struct i915_request *rq;
 
-	lockdep_assert_held(&dev_priv->drm.struct_mutex);
-
 	if (workload->req)
 		return 0;
 

drivers/gpu/drm/i915/i915_active.c

@@ -12,8 +12,6 @@
 #include "i915_active.h"
 #include "i915_globals.h"
 
-#define BKL(ref) (&(ref)->i915->drm.struct_mutex)
-
 /*
  * Active refs memory management
  *
@@ -27,35 +25,35 @@ static struct i915_global_active {
 } global;
 
 struct active_node {
-	struct i915_active_request base;
+	struct i915_active_fence base;
 	struct i915_active *ref;
 	struct rb_node node;
 	u64 timeline;
 };
 
 static inline struct active_node *
-node_from_active(struct i915_active_request *active)
+node_from_active(struct i915_active_fence *active)
 {
 	return container_of(active, struct active_node, base);
 }
 
 #define take_preallocated_barriers(x) llist_del_all(&(x)->preallocated_barriers)
 
-static inline bool is_barrier(const struct i915_active_request *active)
+static inline bool is_barrier(const struct i915_active_fence *active)
 {
-	return IS_ERR(rcu_access_pointer(active->request));
+	return IS_ERR(rcu_access_pointer(active->fence));
 }
 
 static inline struct llist_node *barrier_to_ll(struct active_node *node)
 {
 	GEM_BUG_ON(!is_barrier(&node->base));
-	return (struct llist_node *)&node->base.link;
+	return (struct llist_node *)&node->base.cb.node;
 }
 
 static inline struct intel_engine_cs *
 __barrier_to_engine(struct active_node *node)
 {
-	return (struct intel_engine_cs *)READ_ONCE(node->base.link.prev);
+	return (struct intel_engine_cs *)READ_ONCE(node->base.cb.node.prev);
 }
 
 static inline struct intel_engine_cs *
@@ -68,7 +66,7 @@ barrier_to_engine(struct active_node *node)
 static inline struct active_node *barrier_from_ll(struct llist_node *x)
 {
 	return container_of((struct list_head *)x,
-			    struct active_node, base.link);
+			    struct active_node, base.cb.node);
 }
 
 #if IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM) && IS_ENABLED(CONFIG_DEBUG_OBJECTS)
@@ -147,15 +145,18 @@ __active_retire(struct i915_active *ref)
 	if (!retire)
 		return;
 
-	GEM_BUG_ON(rcu_access_pointer(ref->excl));
+	GEM_BUG_ON(rcu_access_pointer(ref->excl.fence));
 	rbtree_postorder_for_each_entry_safe(it, n, &root, node) {
-		GEM_BUG_ON(i915_active_request_isset(&it->base));
+		GEM_BUG_ON(i915_active_fence_isset(&it->base));
 		kmem_cache_free(global.slab_cache, it);
 	}
 
 	/* After the final retire, the entire struct may be freed */
 	if (ref->retire)
 		ref->retire(ref);
+
+	/* ... except if you wait on it, you must manage your own references! */
+	wake_up_var(ref);
 }
 
 static void
@@ -189,12 +190,20 @@ active_retire(struct i915_active *ref)
 }
 
 static void
-node_retire(struct i915_active_request *base, struct i915_request *rq)
+node_retire(struct dma_fence *fence, struct dma_fence_cb *cb)
 {
-	active_retire(node_from_active(base)->ref);
+	i915_active_fence_cb(fence, cb);
+	active_retire(container_of(cb, struct active_node, base.cb)->ref);
 }
 
-static struct i915_active_request *
+static void
+excl_retire(struct dma_fence *fence, struct dma_fence_cb *cb)
+{
+	i915_active_fence_cb(fence, cb);
+	active_retire(container_of(cb, struct i915_active, excl.cb));
+}
+
+static struct i915_active_fence *
 active_instance(struct i915_active *ref, struct intel_timeline *tl)
 {
 	struct active_node *node, *prealloc;
@@ -238,7 +247,7 @@ active_instance(struct i915_active *ref, struct intel_timeline *tl)
 	}
 
 	node = prealloc;
-	i915_active_request_init(&node->base, &tl->mutex, NULL, node_retire);
+	__i915_active_fence_init(&node->base, &tl->mutex, NULL, node_retire);
 	node->ref = ref;
 	node->timeline = idx;
 
@@ -253,8 +262,7 @@ active_instance(struct i915_active *ref, struct intel_timeline *tl)
 	return &node->base;
 }
 
-void __i915_active_init(struct drm_i915_private *i915,
-			struct i915_active *ref,
+void __i915_active_init(struct i915_active *ref,
 			int (*active)(struct i915_active *ref),
 			void (*retire)(struct i915_active *ref),
 			struct lock_class_key *key)
@@ -263,19 +271,18 @@ void __i915_active_init(struct drm_i915_private *i915,
 
 	debug_active_init(ref);
 
-	ref->i915 = i915;
 	ref->flags = 0;
 	ref->active = active;
 	ref->retire = ptr_unpack_bits(retire, &bits, 2);
 	if (bits & I915_ACTIVE_MAY_SLEEP)
 		ref->flags |= I915_ACTIVE_RETIRE_SLEEPS;
 
-	ref->excl = NULL;
 	ref->tree = RB_ROOT;
 	ref->cache = NULL;
 	init_llist_head(&ref->preallocated_barriers);
 	atomic_set(&ref->count, 0);
 	__mutex_init(&ref->mutex, "i915_active", key);
+	__i915_active_fence_init(&ref->excl, &ref->mutex, NULL, excl_retire);
 	INIT_WORK(&ref->work, active_work);
 }
 
@@ -329,9 +336,9 @@ __active_del_barrier(struct i915_active *ref, struct active_node *node)
 
 int i915_active_ref(struct i915_active *ref,
 		    struct intel_timeline *tl,
-		    struct i915_request *rq)
+		    struct dma_fence *fence)
 {
-	struct i915_active_request *active;
+	struct i915_active_fence *active;
 	int err;
 
 	lockdep_assert_held(&tl->mutex);
@@ -354,66 +361,44 @@ int i915_active_ref(struct i915_active *ref,
 		 * request that we want to emit on the kernel_context.
 		 */
 		__active_del_barrier(ref, node_from_active(active));
-		RCU_INIT_POINTER(active->request, NULL);
-		INIT_LIST_HEAD(&active->link);
-	} else {
-		if (!i915_active_request_isset(active))
-			atomic_inc(&ref->count);
+		RCU_INIT_POINTER(active->fence, NULL);
+		atomic_dec(&ref->count);
 	}
-	GEM_BUG_ON(!atomic_read(&ref->count));
-	__i915_active_request_set(active, rq);
+	if (!__i915_active_fence_set(active, fence))
+		atomic_inc(&ref->count);
 
 out:
 	i915_active_release(ref);
 	return err;
 }
 
-static void excl_cb(struct dma_fence *f, struct dma_fence_cb *cb)
-{
-	struct i915_active *ref = container_of(cb, typeof(*ref), excl_cb);
-
-	RCU_INIT_POINTER(ref->excl, NULL);
-	dma_fence_put(f);
-
-	active_retire(ref);
-}
-
 void i915_active_set_exclusive(struct i915_active *ref, struct dma_fence *f)
 {
 	/* We expect the caller to manage the exclusive timeline ordering */
 	GEM_BUG_ON(i915_active_is_idle(ref));
 
-	dma_fence_get(f);
-
-	rcu_read_lock();
-	if (rcu_access_pointer(ref->excl)) {
-		struct dma_fence *old;
-
-		old = dma_fence_get_rcu_safe(&ref->excl);
-		if (old) {
-			if (dma_fence_remove_callback(old, &ref->excl_cb))
-				atomic_dec(&ref->count);
-			dma_fence_put(old);
-		}
-	}
-	rcu_read_unlock();
-
-	atomic_inc(&ref->count);
-	rcu_assign_pointer(ref->excl, f);
+	/*
+	 * As we don't know which mutex the caller is using, we told a small
+	 * lie to the debug code that it is using the i915_active.mutex;
+	 * and now we must stick to that lie.
+	 */
+	mutex_acquire(&ref->mutex.dep_map, 0, 0, _THIS_IP_);
+	if (!__i915_active_fence_set(&ref->excl, f))
+		atomic_inc(&ref->count);
+	mutex_release(&ref->mutex.dep_map, 0, _THIS_IP_);
+}
 
-	if (dma_fence_add_callback(f, &ref->excl_cb, excl_cb)) {
-		RCU_INIT_POINTER(ref->excl, NULL);
-		atomic_dec(&ref->count);
-		dma_fence_put(f);
-	}
+bool i915_active_acquire_if_busy(struct i915_active *ref)
+{
+	debug_active_assert(ref);
+	return atomic_add_unless(&ref->count, 1, 0);
 }
 
 int i915_active_acquire(struct i915_active *ref)
 {
 	int err;
 
-	debug_active_assert(ref);
-	if (atomic_add_unless(&ref->count, 1, 0))
+	if (i915_active_acquire_if_busy(ref))
 		return 0;
 
 	err = mutex_lock_interruptible(&ref->mutex);
@@ -438,121 +423,57 @@ void i915_active_release(struct i915_active *ref)
 	active_retire(ref);
 }
 
-static void __active_ungrab(struct i915_active *ref)
-{
-	clear_and_wake_up_bit(I915_ACTIVE_GRAB_BIT, &ref->flags);
-}
-
-bool i915_active_trygrab(struct i915_active *ref)
+static void enable_signaling(struct i915_active_fence *active)
 {
-	debug_active_assert(ref);
-
-	if (test_and_set_bit(I915_ACTIVE_GRAB_BIT, &ref->flags))
-		return false;
-
-	if (!atomic_add_unless(&ref->count, 1, 0)) {
-		__active_ungrab(ref);
-		return false;
-	}
+	struct dma_fence *fence;
 
-	return true;
-}
-
-void i915_active_ungrab(struct i915_active *ref)
-{
-	GEM_BUG_ON(!test_bit(I915_ACTIVE_GRAB_BIT, &ref->flags));
-
-	active_retire(ref);
-	__active_ungrab(ref);
-}
-
-static int excl_wait(struct i915_active *ref)
-{
-	struct dma_fence *old;
-	int err = 0;
-
-	if (!rcu_access_pointer(ref->excl))
-		return 0;
-
-	rcu_read_lock();
-	old = dma_fence_get_rcu_safe(&ref->excl);
-	rcu_read_unlock();
-	if (old) {
-		err = dma_fence_wait(old, true);
-		dma_fence_put(old);
-	}
+	fence = i915_active_fence_get(active);
+	if (!fence)
+		return;
 
-	return err;
+	dma_fence_enable_sw_signaling(fence);
+	dma_fence_put(fence);
 }
 
 int i915_active_wait(struct i915_active *ref)
 {
 	struct active_node *it, *n;
-	int err;
+	int err = 0;
 
 	might_sleep();
-	might_lock(&ref->mutex);
-
-	if (i915_active_is_idle(ref))
-		return 0;
-
-	err = mutex_lock_interruptible(&ref->mutex);
-	if (err)
-		return err;
 
-	if (!atomic_add_unless(&ref->count, 1, 0)) {
-		mutex_unlock(&ref->mutex);
+	if (!i915_active_acquire_if_busy(ref))
 		return 0;
-	}
-
-	err = excl_wait(ref);
-	if (err)
-		goto out;
 
+	/* Flush lazy signals */
+	enable_signaling(&ref->excl);
 	rbtree_postorder_for_each_entry_safe(it, n, &ref->tree, node) {
-		if (is_barrier(&it->base)) { /* unconnected idle-barrier */
-			err = -EBUSY;
-			break;
-		}
+		if (is_barrier(&it->base)) /* unconnected idle barrier */
+			continue;
 
-		err = i915_active_request_retire(&it->base, BKL(ref));
-		if (err)
-			break;
+		enable_signaling(&it->base);
 	}
+	/* Any fence added after the wait begins will not be auto-signaled */
 
-out:
-	__active_retire(ref);
+	i915_active_release(ref);
 	if (err)
 		return err;
 
-	if (wait_on_bit(&ref->flags, I915_ACTIVE_GRAB_BIT, TASK_KILLABLE))
+	if (wait_var_event_interruptible(ref, i915_active_is_idle(ref)))
 		return -EINTR;
 
-	flush_work(&ref->work);
-	if (!i915_active_is_idle(ref))
-		return -EBUSY;
-
 	return 0;
 }
 
-int i915_request_await_active_request(struct i915_request *rq,
-				      struct i915_active_request *active)
-{
-	struct i915_request *barrier =
-		i915_active_request_raw(active, &rq->i915->drm.struct_mutex);
-
-	return barrier ? i915_request_await_dma_fence(rq, &barrier->fence) : 0;
-}
-
 int i915_request_await_active(struct i915_request *rq, struct i915_active *ref)
 {
 	int err = 0;
 
-	if (rcu_access_pointer(ref->excl)) {
+	if (rcu_access_pointer(ref->excl.fence)) {
 		struct dma_fence *fence;
 
 		rcu_read_lock();
-		fence = dma_fence_get_rcu_safe(&ref->excl);
+		fence = dma_fence_get_rcu_safe(&ref->excl.fence);
 		rcu_read_unlock();
 		if (fence) {
 			err = i915_request_await_dma_fence(rq, fence);
@@ -578,7 +499,7 @@ void i915_active_fini(struct i915_active *ref)
 
 static inline bool is_idle_barrier(struct active_node *node, u64 idx)
 {
-	return node->timeline == idx && !i915_active_request_isset(&node->base);
+	return node->timeline == idx && !i915_active_fence_isset(&node->base);
 }
 
 static struct active_node *reuse_idle_barrier(struct i915_active *ref, u64 idx)
@@ -698,13 +619,13 @@ int i915_active_acquire_preallocate_barrier(struct i915_active *ref,
 			node->base.lock =
 				&engine->kernel_context->timeline->mutex;
 #endif
-			RCU_INIT_POINTER(node->base.request, NULL);
-			node->base.retire = node_retire;
+			RCU_INIT_POINTER(node->base.fence, NULL);
+			node->base.cb.func = node_retire;
 			node->timeline = idx;
 			node->ref = ref;
 		}
 
-		if (!i915_active_request_isset(&node->base)) {
+		if (!i915_active_fence_isset(&node->base)) {
 			/*
 			 * Mark this as being *our* unconnected proto-node.
 			 *
@@ -714,8 +635,8 @@ int i915_active_acquire_preallocate_barrier(struct i915_active *ref,
 			 * and then we can use the rb_node and list pointers
 			 * for our tracking of the pending barrier.
 			 */
-			RCU_INIT_POINTER(node->base.request, ERR_PTR(-EAGAIN));
-			node->base.link.prev = (void *)engine;
+			RCU_INIT_POINTER(node->base.fence, ERR_PTR(-EAGAIN));
+			node->base.cb.node.prev = (void *)engine;
 			atomic_inc(&ref->count);
 		}
 
@@ -782,44 +703,113 @@ void i915_request_add_active_barriers(struct i915_request *rq)
 {
 	struct intel_engine_cs *engine = rq->engine;
 	struct llist_node *node, *next;
+	unsigned long flags;
 
 	GEM_BUG_ON(intel_engine_is_virtual(engine));
 	GEM_BUG_ON(i915_request_timeline(rq) != engine->kernel_context->timeline);
 
+	node = llist_del_all(&engine->barrier_tasks);
+	if (!node)
+		return;
 	/*
 	 * Attach the list of proto-fences to the in-flight request such
 	 * that the parent i915_active will be released when this request
 	 * is retired.
 	 */
-	llist_for_each_safe(node, next, llist_del_all(&engine->barrier_tasks)) {
-		RCU_INIT_POINTER(barrier_from_ll(node)->base.request, rq);
+	spin_lock_irqsave(&rq->lock, flags);
+	llist_for_each_safe(node, next, node) {
+		RCU_INIT_POINTER(barrier_from_ll(node)->base.fence, &rq->fence);
 		smp_wmb(); /* serialise with reuse_idle_barrier */
-		list_add_tail((struct list_head *)node, &rq->active_list);
+		list_add_tail((struct list_head *)node, &rq->fence.cb_list);
+	}
+	spin_unlock_irqrestore(&rq->lock, flags);
+}
+
+#if IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM)
+#define active_is_held(active) lockdep_is_held((active)->lock)
+#else
+#define active_is_held(active) true
+#endif
+
+/*
+ * __i915_active_fence_set: Update the last active fence along its timeline
+ * @active: the active tracker
+ * @fence: the new fence (under construction)
+ *
+ * Records the new @fence as the last active fence along its timeline in
+ * this active tracker, moving the tracking callbacks from the previous
+ * fence onto this one. Returns the previous fence (if not already completed),
+ * which the caller must ensure is executed before the new fence. To ensure
+ * that the order of fences within the timeline of the i915_active_fence is
+ * maintained, it must be locked by the caller.
+ */
+struct dma_fence *
+__i915_active_fence_set(struct i915_active_fence *active,
+			struct dma_fence *fence)
+{
+	struct dma_fence *prev;
+	unsigned long flags;
+
+	/* NB: must be serialised by an outer timeline mutex (active->lock) */
+	spin_lock_irqsave(fence->lock, flags);
+	GEM_BUG_ON(test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags));
+
+	prev = rcu_dereference_protected(active->fence, active_is_held(active));
+	if (prev) {
+		GEM_BUG_ON(prev == fence);
+		spin_lock_nested(prev->lock, SINGLE_DEPTH_NESTING);
+		__list_del_entry(&active->cb.node);
+		spin_unlock(prev->lock); /* serialise with prev->cb_list */
+
+		/*
+		 * active->fence is reset by the callback from inside
+		 * interrupt context. We need to serialise our list
+		 * manipulation with the fence->lock to prevent the prev
+		 * being lost inside an interrupt (it can't be replaced as
+		 * no other caller is allowed to enter __i915_active_fence_set
+		 * as we hold the timeline lock). After serialising with
+		 * the callback, we need to double check which ran first,
+		 * our list_del() [decoupling prev from the callback] or
+		 * the callback...
+		 */
+		prev = rcu_access_pointer(active->fence);
 	}
+
+	rcu_assign_pointer(active->fence, fence);
+	list_add_tail(&active->cb.node, &fence->cb_list);
+
+	spin_unlock_irqrestore(fence->lock, flags);
+
+	return prev;
 }
 
-int i915_active_request_set(struct i915_active_request *active,
-			    struct i915_request *rq)
+int i915_active_fence_set(struct i915_active_fence *active,
+			  struct i915_request *rq)
 {
-	int err;
+	struct dma_fence *fence;
+	int err = 0;
 
 #if IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM)
 	lockdep_assert_held(active->lock);
 #endif
 
-	/* Must maintain ordering wrt previous active requests */
-	err = i915_request_await_active_request(rq, active);
-	if (err)
-		return err;
+	/* Must maintain timeline ordering wrt previous active requests */
+	rcu_read_lock();
+	fence = __i915_active_fence_set(active, &rq->fence);
+	if (fence) /* but the previous fence may not belong to that timeline! */
+		fence = dma_fence_get_rcu(fence);
+	rcu_read_unlock();
+	if (fence) {
+		err = i915_request_await_dma_fence(rq, fence);
+		dma_fence_put(fence);
+	}
 
-	__i915_active_request_set(active, rq);
-	return 0;
+	return err;
 }
 
-void i915_active_retire_noop(struct i915_active_request *active,
-			     struct i915_request *request)
+void i915_active_noop(struct dma_fence *fence, struct dma_fence_cb *cb)
 {
-	/* Space left intentionally blank */
+	i915_active_fence_cb(fence, cb);
 }
 
 #if IS_ENABLED(CONFIG_DRM_I915_SELFTEST)

drivers/gpu/drm/i915/i915_active.h

@@ -12,6 +12,10 @@
 #include "i915_active_types.h"
 #include "i915_request.h"
 
+struct i915_request;
+struct intel_engine_cs;
+struct intel_timeline;
+
 /*
  * We treat requests as fences. This is not be to confused with our
  * "fence registers" but pipeline synchronisation objects ala GL_ARB_sync.
@@ -28,308 +32,108 @@
  * write access so that we can perform concurrent read operations between
  * the CPU and GPU engines, as well as waiting for all rendering to
  * complete, or waiting for the last GPU user of a "fence register". The
- * object then embeds a #i915_active_request to track the most recent (in
+ * object then embeds a #i915_active_fence to track the most recent (in
  * retirement order) request relevant for the desired mode of access.
- * The #i915_active_request is updated with i915_active_request_set() to
+ * The #i915_active_fence is updated with i915_active_fence_set() to
  * track the most recent fence request, typically this is done as part of
  * i915_vma_move_to_active().
  *
- * When the #i915_active_request completes (is retired), it will
+ * When the #i915_active_fence completes (is retired), it will
  * signal its completion to the owner through a callback as well as mark
- * itself as idle (i915_active_request.request == NULL). The owner
+ * itself as idle (i915_active_fence.request == NULL). The owner
  * can then perform any action, such as delayed freeing of an active
  * resource including itself.
  */
 
-void i915_active_retire_noop(struct i915_active_request *active,
-			     struct i915_request *request);
+void i915_active_noop(struct dma_fence *fence, struct dma_fence_cb *cb);
 
 /**
- * i915_active_request_init - prepares the activity tracker for use
+ * __i915_active_fence_init - prepares the activity tracker for use
  * @active - the active tracker
- * @rq - initial request to track, can be NULL
+ * @fence - initial fence to track, can be NULL
  * @func - a callback when then the tracker is retired (becomes idle),
  *         can be NULL
  *
- * i915_active_request_init() prepares the embedded @active struct for use as
- * an activity tracker, that is for tracking the last known active request
- * associated with it. When the last request becomes idle, when it is retired
+ * i915_active_fence_init() prepares the embedded @active struct for use as
+ * an activity tracker, that is for tracking the last known active fence
+ * associated with it. When the last fence becomes idle, when it is retired
  * after completion, the optional callback @func is invoked.
  */
 static inline void
-i915_active_request_init(struct i915_active_request *active,
+__i915_active_fence_init(struct i915_active_fence *active,
 			 struct mutex *lock,
-			 struct i915_request *rq,
-			 i915_active_retire_fn retire)
+			 void *fence,
+			 dma_fence_func_t fn)
 {
-	RCU_INIT_POINTER(active->request, rq);
-	INIT_LIST_HEAD(&active->link);
-	active->retire = retire ?: i915_active_retire_noop;
+	RCU_INIT_POINTER(active->fence, fence);
+	active->cb.func = fn ?: i915_active_noop;
 #if IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM)
 	active->lock = lock;
 #endif
 }
 
-#define INIT_ACTIVE_REQUEST(name, lock) \
-	i915_active_request_init((name), (lock), NULL, NULL)
-
-/**
- * i915_active_request_set - updates the tracker to watch the current request
- * @active - the active tracker
- * @request - the request to watch
- *
- * __i915_active_request_set() watches the given @request for completion. Whilst
- * that @request is busy, the @active reports busy. When that @request is
- * retired, the @active tracker is updated to report idle.
- */
-static inline void
-__i915_active_request_set(struct i915_active_request *active,
-			  struct i915_request *request)
-{
-#if IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM)
-	lockdep_assert_held(active->lock);
-#endif
-	list_move(&active->link, &request->active_list);
-	rcu_assign_pointer(active->request, request);
-}
+#define INIT_ACTIVE_FENCE(A, LOCK) \
+	__i915_active_fence_init((A), (LOCK), NULL, NULL)
 
-int __must_check
-i915_active_request_set(struct i915_active_request *active,
-			struct i915_request *rq);
+struct dma_fence *
+__i915_active_fence_set(struct i915_active_fence *active,
+			struct dma_fence *fence);
 
 /**
- * i915_active_request_raw - return the active request
+ * i915_active_fence_set - updates the tracker to watch the current fence
  * @active - the active tracker
+ * @rq - the request to watch
  *
- * i915_active_request_raw() returns the current request being tracked, or NULL.
- * It does not obtain a reference on the request for the caller, so the caller
- * must hold struct_mutex.
+ * i915_active_fence_set() watches the given @rq for completion. While
+ * that @rq is busy, the @active reports busy. When that @rq is signaled
+ * (or else retired) the @active tracker is updated to report idle.
  */
-static inline struct i915_request *
-i915_active_request_raw(const struct i915_active_request *active,
-			struct mutex *mutex)
-{
-	return rcu_dereference_protected(active->request,
-					 lockdep_is_held(mutex));
-}
-
-/**
- * i915_active_request_peek - report the active request being monitored
- * @active - the active tracker
- *
- * i915_active_request_peek() returns the current request being tracked if
- * still active, or NULL. It does not obtain a reference on the request
- * for the caller, so the caller must hold struct_mutex.
- */
-static inline struct i915_request *
-i915_active_request_peek(const struct i915_active_request *active,
-			 struct mutex *mutex)
-{
-	struct i915_request *request;
-
-	request = i915_active_request_raw(active, mutex);
-	if (!request || i915_request_completed(request))
-		return NULL;
-
-	return request;
-}
-
-/**
- * i915_active_request_get - return a reference to the active request
- * @active - the active tracker
- *
- * i915_active_request_get() returns a reference to the active request, or NULL
- * if the active tracker is idle. The caller must hold struct_mutex.
- */
-static inline struct i915_request *
-i915_active_request_get(const struct i915_active_request *active,
-			struct mutex *mutex)
-{
-	return i915_request_get(i915_active_request_peek(active, mutex));
-}
-
-/**
- * __i915_active_request_get_rcu - return a reference to the active request
- * @active - the active tracker
- *
- * __i915_active_request_get() returns a reference to the active request,
- * or NULL if the active tracker is idle. The caller must hold the RCU read
- * lock, but the returned pointer is safe to use outside of RCU.
- */
-static inline struct i915_request *
-__i915_active_request_get_rcu(const struct i915_active_request *active)
-{
-	/*
-	 * Performing a lockless retrieval of the active request is super
-	 * tricky. SLAB_TYPESAFE_BY_RCU merely guarantees that the backing
-	 * slab of request objects will not be freed whilst we hold the
-	 * RCU read lock. It does not guarantee that the request itself
-	 * will not be freed and then *reused*. Viz,
-	 *
-	 * Thread A			Thread B
-	 *
-	 * rq = active.request
-	 *				retire(rq) -> free(rq);
-	 *				(rq is now first on the slab freelist)
-	 *				active.request = NULL
-	 *
-	 *				rq = new submission on a new object
-	 * ref(rq)
-	 *
-	 * To prevent the request from being reused whilst the caller
-	 * uses it, we take a reference like normal. Whilst acquiring
-	 * the reference we check that it is not in a destroyed state
-	 * (refcnt == 0). That prevents the request being reallocated
-	 * whilst the caller holds on to it. To check that the request
-	 * was not reallocated as we acquired the reference we have to
-	 * check that our request remains the active request across
-	 * the lookup, in the same manner as a seqlock. The visibility
-	 * of the pointer versus the reference counting is controlled
-	 * by using RCU barriers (rcu_dereference and rcu_assign_pointer).
-	 *
-	 * In the middle of all that, we inspect whether the request is
-	 * complete. Retiring is lazy so the request may be completed long
-	 * before the active tracker is updated. Querying whether the
-	 * request is complete is far cheaper (as it involves no locked
-	 * instructions setting cachelines to exclusive) than acquiring
-	 * the reference, so we do it first. The RCU read lock ensures the
-	 * pointer dereference is valid, but does not ensure that the
-	 * seqno nor HWS is the right one! However, if the request was
-	 * reallocated, that means the active tracker's request was complete.
-	 * If the new request is also complete, then both are and we can
-	 * just report the active tracker is idle. If the new request is
-	 * incomplete, then we acquire a reference on it and check that
-	 * it remained the active request.
-	 *
-	 * It is then imperative that we do not zero the request on
-	 * reallocation, so that we can chase the dangling pointers!
-	 * See i915_request_alloc().
-	 */
-	do {
-		struct i915_request *request;
-
-		request = rcu_dereference(active->request);
-		if (!request || i915_request_completed(request))
-			return NULL;
-
-		/*
-		 * An especially silly compiler could decide to recompute the
-		 * result of i915_request_completed, more specifically
-		 * re-emit the load for request->fence.seqno. A race would catch
-		 * a later seqno value, which could flip the result from true to
-		 * false. Which means part of the instructions below might not
-		 * be executed, while later on instructions are executed. Due to
-		 * barriers within the refcounting the inconsistency can't reach
-		 * past the call to i915_request_get_rcu, but not executing
-		 * that while still executing i915_request_put() creates
-		 * havoc enough.  Prevent this with a compiler barrier.
-		 */
-		barrier();
-
-		request = i915_request_get_rcu(request);
-
-		/*
-		 * What stops the following rcu_access_pointer() from occurring
-		 * before the above i915_request_get_rcu()? If we were
-		 * to read the value before pausing to get the reference to
-		 * the request, we may not notice a change in the active
-		 * tracker.
-		 *
-		 * The rcu_access_pointer() is a mere compiler barrier, which
-		 * means both the CPU and compiler are free to perform the
-		 * memory read without constraint. The compiler only has to
-		 * ensure that any operations after the rcu_access_pointer()
-		 * occur afterwards in program order. This means the read may
-		 * be performed earlier by an out-of-order CPU, or adventurous
-		 * compiler.
-		 *
-		 * The atomic operation at the heart of
-		 * i915_request_get_rcu(), see dma_fence_get_rcu(), is
-		 * atomic_inc_not_zero() which is only a full memory barrier
-		 * when successful. That is, if i915_request_get_rcu()
-		 * returns the request (and so with the reference counted
-		 * incremented) then the following read for rcu_access_pointer()
-		 * must occur after the atomic operation and so confirm
-		 * that this request is the one currently being tracked.
-		 *
-		 * The corresponding write barrier is part of
-		 * rcu_assign_pointer().
-		 */
-		if (!request || request == rcu_access_pointer(active->request))
-			return rcu_pointer_handoff(request);
-
-		i915_request_put(request);
-	} while (1);
-}
-
+int __must_check
+i915_active_fence_set(struct i915_active_fence *active,
+		      struct i915_request *rq);
 /**
- * i915_active_request_get_unlocked - return a reference to the active request
+ * i915_active_fence_get - return a reference to the active fence
  * @active - the active tracker
  *
- * i915_active_request_get_unlocked() returns a reference to the active request,
+ * i915_active_fence_get() returns a reference to the active fence,
  * or NULL if the active tracker is idle. The reference is obtained under RCU,
  * so no locking is required by the caller.
  *
- * The reference should be freed with i915_request_put().
+ * The reference should be freed with dma_fence_put().
  */
-static inline struct i915_request *
-i915_active_request_get_unlocked(const struct i915_active_request *active)
+static inline struct dma_fence *
+i915_active_fence_get(struct i915_active_fence *active)
 {
-	struct i915_request *request;
+	struct dma_fence *fence;
 
 	rcu_read_lock();
-	request = __i915_active_request_get_rcu(active);
+	fence = dma_fence_get_rcu_safe(&active->fence);
 	rcu_read_unlock();
 
-	return request;
+	return fence;
 }
 
 /**
- * i915_active_request_isset - report whether the active tracker is assigned
+ * i915_active_fence_isset - report whether the active tracker is assigned
  * @active - the active tracker
  *
- * i915_active_request_isset() returns true if the active tracker is currently
- * assigned to a request. Due to the lazy retiring, that request may be idle
+ * i915_active_fence_isset() returns true if the active tracker is currently
+ * assigned to a fence. Due to the lazy retiring, that fence may be idle
  * and this may report stale information.
  */
 static inline bool
-i915_active_request_isset(const struct i915_active_request *active)
+i915_active_fence_isset(const struct i915_active_fence *active)
 {
-	return rcu_access_pointer(active->request);
+	return rcu_access_pointer(active->fence);
 }
 
-/**
- * i915_active_request_retire - waits until the request is retired
- * @active - the active request on which to wait
- *
- * i915_active_request_retire() waits until the request is completed,
- * and then ensures that at least the retirement handler for this
- * @active tracker is called before returning. If the @active
- * tracker is idle, the function returns immediately.
- */
-static inline int __must_check
-i915_active_request_retire(struct i915_active_request *active,
-			   struct mutex *mutex)
+static inline void
+i915_active_fence_cb(struct dma_fence *fence, struct dma_fence_cb *cb)
 {
-	struct i915_request *request;
-	long ret;
-
-	request = i915_active_request_raw(active, mutex);
-	if (!request)
-		return 0;
-
-	ret = i915_request_wait(request,
-				I915_WAIT_INTERRUPTIBLE,
-				MAX_SCHEDULE_TIMEOUT);
-	if (ret < 0)
-		return ret;
+	struct i915_active_fence *active =
+		container_of(cb, typeof(*active), cb);
 
-	list_del_init(&active->link);
-	RCU_INIT_POINTER(active->request, NULL);
-
-	active->retire(active, request);
-
-	return 0;
+	RCU_INIT_POINTER(active->fence, NULL);
 }
 
 /*
@@ -358,47 +162,40 @@ i915_active_request_retire(struct i915_active_request *active,
  * synchronisation.
  */
 
-void __i915_active_init(struct drm_i915_private *i915,
-			struct i915_active *ref,
+void __i915_active_init(struct i915_active *ref,
 			int (*active)(struct i915_active *ref),
 			void (*retire)(struct i915_active *ref),
 			struct lock_class_key *key);
-#define i915_active_init(i915, ref, active, retire) do {		\
+#define i915_active_init(ref, active, retire) do {		\
 	static struct lock_class_key __key;				\
 									\
-	__i915_active_init(i915, ref, active, retire, &__key);		\
+	__i915_active_init(ref, active, retire, &__key);		\
 } while (0)
 
 int i915_active_ref(struct i915_active *ref,
 		    struct intel_timeline *tl,
-		    struct i915_request *rq);
+		    struct dma_fence *fence);
 
 static inline int
 i915_active_add_request(struct i915_active *ref, struct i915_request *rq)
 {
-	return i915_active_ref(ref, i915_request_timeline(rq), rq);
+	return i915_active_ref(ref, i915_request_timeline(rq), &rq->fence);
 }
 
 void i915_active_set_exclusive(struct i915_active *ref, struct dma_fence *f);
 
 static inline bool i915_active_has_exclusive(struct i915_active *ref)
 {
-	return rcu_access_pointer(ref->excl);
+	return rcu_access_pointer(ref->excl.fence);
 }
 
 int i915_active_wait(struct i915_active *ref);
 
-int i915_request_await_active(struct i915_request *rq,
-			      struct i915_active *ref);
-int i915_request_await_active_request(struct i915_request *rq,
-				      struct i915_active_request *active);
+int i915_request_await_active(struct i915_request *rq, struct i915_active *ref);
 
 int i915_active_acquire(struct i915_active *ref);
+bool i915_active_acquire_if_busy(struct i915_active *ref);
 void i915_active_release(struct i915_active *ref);
-void __i915_active_release_nested(struct i915_active *ref, int subclass);
-
-bool i915_active_trygrab(struct i915_active *ref);
-void i915_active_ungrab(struct i915_active *ref);
 
 static inline bool
 i915_active_is_idle(const struct i915_active *ref)

drivers/gpu/drm/i915/i915_active_types.h

@@ -17,17 +17,9 @@
 
 #include "i915_utils.h"
 
-struct drm_i915_private;
-struct i915_active_request;
-struct i915_request;
-
-typedef void (*i915_active_retire_fn)(struct i915_active_request *,
-				      struct i915_request *);
-
-struct i915_active_request {
-	struct i915_request __rcu *request;
-	struct list_head link;
-	i915_active_retire_fn retire;
+struct i915_active_fence {
+	struct dma_fence __rcu *fence;
+	struct dma_fence_cb cb;
 #if IS_ENABLED(CONFIG_DRM_I915_DEBUG_GEM)
 	/*
 	 * Incorporeal!
@@ -53,20 +45,17 @@ struct active_node;
 #define i915_active_may_sleep(fn) ptr_pack_bits(&(fn), I915_ACTIVE_MAY_SLEEP, 2)
 
 struct i915_active {
-	struct drm_i915_private *i915;
+	atomic_t count;
+	struct mutex mutex;
 
 	struct active_node *cache;
 	struct rb_root tree;
-	struct mutex mutex;
-	atomic_t count;
 
 	/* Preallocated "exclusive" node */
-	struct dma_fence __rcu *excl;
-	struct dma_fence_cb excl_cb;
+	struct i915_active_fence excl;
 
 	unsigned long flags;
 #define I915_ACTIVE_RETIRE_SLEEPS BIT(0)
-#define I915_ACTIVE_GRAB_BIT 1
 
 	int (*active)(struct i915_active *ref);
 	void (*retire)(struct i915_active *ref);

drivers/gpu/drm/i915/i915_gem.c

@@ -892,28 +892,38 @@ wait_for_timelines(struct intel_gt *gt, unsigned int wait, long timeout)
 
 	spin_lock_irqsave(&timelines->lock, flags);
 	list_for_each_entry(tl, &timelines->active_list, link) {
-		struct i915_request *rq;
+		struct dma_fence *fence;
 
-		rq = i915_active_request_get_unlocked(&tl->last_request);
-		if (!rq)
+		fence = i915_active_fence_get(&tl->last_request);
+		if (!fence)
 			continue;
 
 		spin_unlock_irqrestore(&timelines->lock, flags);
 
-		/*
-		 * "Race-to-idle".
-		 *
-		 * Switching to the kernel context is often used a synchronous
-		 * step prior to idling, e.g. in suspend for flushing all
-		 * current operations to memory before sleeping. These we
-		 * want to complete as quickly as possible to avoid prolonged
-		 * stalls, so allow the gpu to boost to maximum clocks.
-		 */
-		if (wait & I915_WAIT_FOR_IDLE_BOOST)
-			gen6_rps_boost(rq);
+		if (!dma_fence_is_i915(fence)) {
+			timeout = dma_fence_wait_timeout(fence,
+							 flags & I915_WAIT_INTERRUPTIBLE,
+							 timeout);
+		} else {
+			struct i915_request *rq = to_request(fence);
+
+			/*
+			 * "Race-to-idle".
+			 *
+			 * Switching to the kernel context is often used as
+			 * a synchronous step prior to idling, e.g. in suspend
+			 * for flushing all current operations to memory before
+			 * sleeping. These we want to complete as quickly as
+			 * possible to avoid prolonged stalls, so allow the gpu
+			 * to boost to maximum clocks.
+			 */
+			if (flags & I915_WAIT_FOR_IDLE_BOOST)
+				gen6_rps_boost(rq);
+
+			timeout = i915_request_wait(rq, flags, timeout);
+		}
 
-		timeout = i915_request_wait(rq, wait, timeout);
-		i915_request_put(rq);
+		dma_fence_put(fence);
 		if (timeout < 0)
 			return timeout;
 

drivers/gpu/drm/i915/i915_gem_gtt.c

@@ -1861,7 +1861,6 @@ static const struct i915_vma_ops pd_vma_ops = {
 
 static struct i915_vma *pd_vma_create(struct gen6_ppgtt *ppgtt, int size)
 {
-	struct drm_i915_private *i915 = ppgtt->base.vm.i915;
 	struct i915_ggtt *ggtt = ppgtt->base.vm.gt->ggtt;
 	struct i915_vma *vma;
 
@@ -1872,7 +1871,7 @@ static struct i915_vma *pd_vma_create(struct gen6_ppgtt *ppgtt, int size)
 	if (!vma)
 		return ERR_PTR(-ENOMEM);
 
-	i915_active_init(i915, &vma->active, NULL, NULL);
+	i915_active_init(&vma->active, NULL, NULL);
 
 	mutex_init(&vma->pages_mutex);
 	vma->vm = i915_vm_get(&ggtt->vm);

drivers/gpu/drm/i915/i915_gpu_error.c

@@ -1299,7 +1299,7 @@ capture_vma(struct capture_vma *next,
 	if (!c)
 		return next;
 
-	if (!i915_active_trygrab(&vma->active)) {
+	if (!i915_active_acquire_if_busy(&vma->active)) {
 		kfree(c);
 		return next;
 	}
@@ -1439,7 +1439,7 @@ gem_record_rings(struct i915_gpu_state *error, struct compress *compress)
 			*this->slot =
 				i915_error_object_create(i915, vma, compress);
 
-			i915_active_ungrab(&vma->active);
+			i915_active_release(&vma->active);
 			i915_vma_put(vma);
 
 			capture = this->next;

drivers/gpu/drm/i915/i915_request.c

@@ -218,8 +218,6 @@ static void remove_from_engine(struct i915_request *rq)
 
 static bool i915_request_retire(struct i915_request *rq)
 {
-	struct i915_active_request *active, *next;
-
 	if (!i915_request_completed(rq))
 		return false;
 
@@ -244,35 +242,6 @@ static bool i915_request_retire(struct i915_request *rq)
 				  &i915_request_timeline(rq)->requests));
 	rq->ring->head = rq->postfix;
 
-	/*
-	 * Walk through the active list, calling retire on each. This allows
-	 * objects to track their GPU activity and mark themselves as idle
-	 * when their *last* active request is completed (updating state
-	 * tracking lists for eviction, active references for GEM, etc).
-	 *
-	 * As the ->retire() may free the node, we decouple it first and
-	 * pass along the auxiliary information (to avoid dereferencing
-	 * the node after the callback).
-	 */
-	list_for_each_entry_safe(active, next, &rq->active_list, link) {
-		/*
-		 * In microbenchmarks or focusing upon time inside the kernel,
-		 * we may spend an inordinate amount of time simply handling
-		 * the retirement of requests and processing their callbacks.
-		 * Of which, this loop itself is particularly hot due to the
-		 * cache misses when jumping around the list of
-		 * i915_active_request.  So we try to keep this loop as
-		 * streamlined as possible and also prefetch the next
-		 * i915_active_request to try and hide the likely cache miss.
-		 */
-		prefetchw(next);
-
-		INIT_LIST_HEAD(&active->link);
-		RCU_INIT_POINTER(active->request, NULL);
-
-		active->retire(active, rq);
-	}
-
 	local_irq_disable();
 
 	/*
@@ -704,7 +673,6 @@ __i915_request_create(struct intel_context *ce, gfp_t gfp)
 	rq->flags = 0;
 	rq->execution_mask = ALL_ENGINES;
 
-	INIT_LIST_HEAD(&rq->active_list);
 	INIT_LIST_HEAD(&rq->execute_cb);
 
 	/*
@@ -743,7 +711,6 @@ __i915_request_create(struct intel_context *ce, gfp_t gfp)
 	ce->ring->emit = rq->head;
 
 	/* Make sure we didn't add ourselves to external state before freeing */
-	GEM_BUG_ON(!list_empty(&rq->active_list));
 	GEM_BUG_ON(!list_empty(&rq->sched.signalers_list));
 	GEM_BUG_ON(!list_empty(&rq->sched.waiters_list));
 
@@ -1174,8 +1141,8 @@ __i915_request_add_to_timeline(struct i915_request *rq)
 	 * precludes optimising to use semaphores serialisation of a single
 	 * timeline across engines.
 	 */
-	prev = rcu_dereference_protected(timeline->last_request.request,
-					 lockdep_is_held(&timeline->mutex));
+	prev = to_request(__i915_active_fence_set(&timeline->last_request,
+						  &rq->fence));
 	if (prev && !i915_request_completed(prev)) {
 		if (is_power_of_2(prev->engine->mask | rq->engine->mask))
 			i915_sw_fence_await_sw_fence(&rq->submit,
@@ -1200,7 +1167,6 @@ __i915_request_add_to_timeline(struct i915_request *rq)
 	 * us, the timeline will hold its seqno which is later than ours.
 	 */
 	GEM_BUG_ON(timeline->seqno != rq->fence.seqno);
-	__i915_active_request_set(&timeline->last_request, rq);
 
 	return prev;
 }

drivers/gpu/drm/i915/i915_request.h

@@ -211,7 +211,6 @@ struct i915_request {
 	 * on the active_list (of their final request).
 	 */
 	struct i915_capture_list *capture_list;
-	struct list_head active_list;
 
 	/** Time at which this request was emitted, in jiffies. */
 	unsigned long emitted_jiffies;

drivers/gpu/drm/i915/i915_vma.c

@@ -120,8 +120,7 @@ vma_create(struct drm_i915_gem_object *obj,
 	vma->size = obj->base.size;
 	vma->display_alignment = I915_GTT_MIN_ALIGNMENT;
 
-	i915_active_init(vm->i915, &vma->active,
-			 __i915_vma_active, __i915_vma_retire);
+	i915_active_init(&vma->active, __i915_vma_active, __i915_vma_retire);
 
 	/* Declare ourselves safe for use inside shrinkers */
 	if (IS_ENABLED(CONFIG_LOCKDEP)) {
@@ -1148,6 +1147,7 @@ int __i915_vma_unbind(struct i915_vma *vma)
 	if (ret)
 		return ret;
 
+	GEM_BUG_ON(i915_vma_is_active(vma));
 	if (i915_vma_is_pinned(vma)) {
 		vma_print_allocator(vma, "is pinned");
 		return -EBUSY;

drivers/gpu/drm/i915/selftests/i915_active.c

@@ -68,7 +68,7 @@ static struct live_active *__live_alloc(struct drm_i915_private *i915)
 		return NULL;
 
 	kref_init(&active->ref);
-	i915_active_init(i915, &active->base, __live_active, __live_retire);
+	i915_active_init(&active->base, __live_active, __live_retire);
 
 	return active;
 }
@@ -146,19 +146,13 @@ static int live_active_wait(void *arg)
 {
 	struct drm_i915_private *i915 = arg;
 	struct live_active *active;
-	intel_wakeref_t wakeref;
 	int err = 0;
 
 	/* Check that we get a callback when requests retire upon waiting */
 
-	mutex_lock(&i915->drm.struct_mutex);
-	wakeref = intel_runtime_pm_get(&i915->runtime_pm);
-
 	active = __live_active_setup(i915);
-	if (IS_ERR(active)) {
-		err = PTR_ERR(active);
-		goto err;
-	}
+	if (IS_ERR(active))
+		return PTR_ERR(active);
 
 	i915_active_wait(&active->base);
 	if (!READ_ONCE(active->retired)) {
@@ -168,11 +162,9 @@ static int live_active_wait(void *arg)
 
 	__live_put(active);
 
+	mutex_lock(&i915->drm.struct_mutex);
 	if (igt_flush_test(i915, I915_WAIT_LOCKED))
 		err = -EIO;
-
-err:
-	intel_runtime_pm_put(&i915->runtime_pm, wakeref);
 	mutex_unlock(&i915->drm.struct_mutex);
 
 	return err;
@@ -182,23 +174,19 @@ static int live_active_retire(void *arg)
 {
 	struct drm_i915_private *i915 = arg;
 	struct live_active *active;
-	intel_wakeref_t wakeref;
 	int err = 0;
 
 	/* Check that we get a callback when requests are indirectly retired */
 
-	mutex_lock(&i915->drm.struct_mutex);
-	wakeref = intel_runtime_pm_get(&i915->runtime_pm);
-
 	active = __live_active_setup(i915);
-	if (IS_ERR(active)) {
-		err = PTR_ERR(active);
-		goto err;
-	}
+	if (IS_ERR(active))
+		return PTR_ERR(active);
 
 	/* waits for & retires all requests */
+	mutex_lock(&i915->drm.struct_mutex);
 	if (igt_flush_test(i915, I915_WAIT_LOCKED))
 		err = -EIO;
+	mutex_unlock(&i915->drm.struct_mutex);
 
 	if (!READ_ONCE(active->retired)) {
 		pr_err("i915_active not retired after flushing!\n");
@@ -207,10 +195,6 @@ static int live_active_retire(void *arg)
 
 	__live_put(active);
 
-err:
-	intel_runtime_pm_put(&i915->runtime_pm, wakeref);
-	mutex_unlock(&i915->drm.struct_mutex);
-
 	return err;
 }