drm: Revert syncobj timeline changes.

Daniel suggested I submit this, since we're still seeing regressions
from it.  This is a revert to before 48197bc5 ("drm: add syncobj
timeline support v9") and its followon fixes.

Fixes this on first V3D testcase execution:

[   48.767088] ============================================
[   48.772410] WARNING: possible recursive locking detected
[   48.777739] 4.19.0-rc6+ #489 Not tainted
[   48.781668] --------------------------------------------
[   48.786993] shader_runner/3284 is trying to acquire lock:
[   48.792408] ce309d7f (&(&array->lock)->rlock){....}, at: dma_fence_add_callback+0x30/0x23c
[   48.800714]
[   48.800714] but task is already holding lock:
[   48.806559] c5952bd3 (&(&array->lock)->rlock){....}, at: dma_fence_add_callback+0x30/0x23c
[   48.814862]
[   48.814862] other info that might help us debug this:
[   48.821410]  Possible unsafe locking scenario:
[   48.821410]
[   48.827338]        CPU0
[   48.829788]        ----
[   48.832239]   lock(&(&array->lock)->rlock);
[   48.836434]   lock(&(&array->lock)->rlock);
[   48.840640]
[   48.840640]  *** DEADLOCK ***
[   48.840640]
[   48.846582]  May be due to missing lock nesting notation
[  130.763560] 1 lock held by cts-runner/3270:
[  130.767745]  #0: 7834b793 (&(&array->lock)->rlock){-...}, at: dma_fence_add_callback+0x30/0x23c
[  130.776461]
               stack backtrace:
[  130.780825] CPU: 1 PID: 3270 Comm: cts-runner Not tainted 4.19.0-rc6+ #486
[  130.787706] Hardware name: Broadcom STB (Flattened Device Tree)
[  130.793645] [<c021269c>] (unwind_backtrace) from [<c020db1c>] (show_stack+0x10/0x14)
[  130.801404] [<c020db1c>] (show_stack) from [<c0c2c4b0>] (dump_stack+0xa8/0xd4)
[  130.808642] [<c0c2c4b0>] (dump_stack) from [<c0281a84>] (__lock_acquire+0x848/0x1a68)
[  130.816483] [<c0281a84>] (__lock_acquire) from [<c02835d8>] (lock_acquire+0xd8/0x22c)
[  130.824326] [<c02835d8>] (lock_acquire) from [<c0c49948>] (_raw_spin_lock_irqsave+0x54/0x68)
[  130.832777] [<c0c49948>] (_raw_spin_lock_irqsave) from [<c086bf54>] (dma_fence_add_callback+0x30/0x23c)
[  130.842183] [<c086bf54>] (dma_fence_add_callback) from [<c086d4c8>] (dma_fence_array_enable_signaling+0x58/0xec)
[  130.852371] [<c086d4c8>] (dma_fence_array_enable_signaling) from [<c086c00c>] (dma_fence_add_callback+0xe8/0x23c)
[  130.862647] [<c086c00c>] (dma_fence_add_callback) from [<c06d8774>] (drm_syncobj_wait_ioctl+0x518/0x614)
[  130.872143] [<c06d8774>] (drm_syncobj_wait_ioctl) from [<c06b8458>] (drm_ioctl_kernel+0xb0/0xf0)
[  130.880940] [<c06b8458>] (drm_ioctl_kernel) from [<c06b8818>] (drm_ioctl+0x1d8/0x390)
[  130.888782] [<c06b8818>] (drm_ioctl) from [<c03a4510>] (do_vfs_ioctl+0xb0/0x8ac)
[  130.896187] [<c03a4510>] (do_vfs_ioctl) from [<c03a4d40>] (ksys_ioctl+0x34/0x60)
[  130.903593] [<c03a4d40>] (ksys_ioctl) from [<c0201000>] (ret_fast_syscall+0x0/0x28)

Cc: Chunming Zhou <david1.zhou@amd.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Eric Anholt <eric@anholt.net>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/261044/

drivers/gpu/drm/drm_syncobj.c

@@ -56,9 +56,6 @@
 #include "drm_internal.h"
 #include <drm/drm_syncobj.h>
 
-/* merge normal syncobj to timeline syncobj, the point interval is 1 */
-#define DRM_SYNCOBJ_BINARY_POINT 1
-
 struct drm_syncobj_stub_fence {
 	struct dma_fence base;
 	spinlock_t lock;
@@ -74,29 +71,7 @@ static const struct dma_fence_ops drm_syncobj_stub_fence_ops = {
 	.get_timeline_name = drm_syncobj_stub_fence_get_name,
 };
 
-struct drm_syncobj_signal_pt {
-	struct dma_fence_array *fence_array;
-	u64    value;
-	struct list_head list;
-};
-
-static DEFINE_SPINLOCK(signaled_fence_lock);
-static struct dma_fence signaled_fence;
-
-static struct dma_fence *drm_syncobj_get_stub_fence(void)
-{
-	spin_lock(&signaled_fence_lock);
-	if (!signaled_fence.ops) {
-		dma_fence_init(&signaled_fence,
-			       &drm_syncobj_stub_fence_ops,
-			       &signaled_fence_lock,
-			       0, 0);
-		dma_fence_signal_locked(&signaled_fence);
-	}
-	spin_unlock(&signaled_fence_lock);
 
-	return dma_fence_get(&signaled_fence);
-}
 /**
  * drm_syncobj_find - lookup and reference a sync object.
  * @file_private: drm file private pointer
@@ -123,27 +98,6 @@ struct drm_syncobj *drm_syncobj_find(struct drm_file *file_private,
 }
 EXPORT_SYMBOL(drm_syncobj_find);
 
-static struct dma_fence *
-drm_syncobj_find_signal_pt_for_point(struct drm_syncobj *syncobj,
-				     uint64_t point)
-{
-	struct drm_syncobj_signal_pt *signal_pt;
-
-	if ((syncobj->type == DRM_SYNCOBJ_TYPE_TIMELINE) &&
-	    (point <= syncobj->timeline))
-		return drm_syncobj_get_stub_fence();
-
-	list_for_each_entry(signal_pt, &syncobj->signal_pt_list, list) {
-		if (point > signal_pt->value)
-			continue;
-		if ((syncobj->type == DRM_SYNCOBJ_TYPE_BINARY) &&
-		    (point != signal_pt->value))
-			continue;
-		return dma_fence_get(&signal_pt->fence_array->base);
-	}
-	return NULL;
-}
-
 static void drm_syncobj_add_callback_locked(struct drm_syncobj *syncobj,
 					    struct drm_syncobj_cb *cb,
 					    drm_syncobj_func_t func)
@@ -152,158 +106,53 @@ static void drm_syncobj_add_callback_locked(struct drm_syncobj *syncobj,
 	list_add_tail(&cb->node, &syncobj->cb_list);
 }
 
-static void drm_syncobj_fence_get_or_add_callback(struct drm_syncobj *syncobj,
+static int drm_syncobj_fence_get_or_add_callback(struct drm_syncobj *syncobj,
 						 struct dma_fence **fence,
 						 struct drm_syncobj_cb *cb,
 						 drm_syncobj_func_t func)
 {
-	u64 pt_value = 0;
-
-	WARN_ON(*fence);
-
-	if (syncobj->type == DRM_SYNCOBJ_TYPE_BINARY) {
-		/*BINARY syncobj always wait on last pt */
-		pt_value = syncobj->signal_point;
+	int ret;
 
-		if (pt_value == 0)
-			pt_value += DRM_SYNCOBJ_BINARY_POINT;
-	}
+	*fence = drm_syncobj_fence_get(syncobj);
+	if (*fence)
+		return 1;
 
-	mutex_lock(&syncobj->cb_mutex);
-	spin_lock(&syncobj->pt_lock);
-	*fence = drm_syncobj_find_signal_pt_for_point(syncobj, pt_value);
-	spin_unlock(&syncobj->pt_lock);
-	if (!*fence)
+	spin_lock(&syncobj->lock);
+	/* We've already tried once to get a fence and failed.  Now that we
+	 * have the lock, try one more time just to be sure we don't add a
+	 * callback when a fence has already been set.
+	 */
+	if (syncobj->fence) {
+		*fence = dma_fence_get(rcu_dereference_protected(syncobj->fence,
+								 lockdep_is_held(&syncobj->lock)));
+		ret = 1;
+	} else {
+		*fence = NULL;
 		drm_syncobj_add_callback_locked(syncobj, cb, func);
-	mutex_unlock(&syncobj->cb_mutex);
-}
-
-static void drm_syncobj_remove_callback(struct drm_syncobj *syncobj,
-					struct drm_syncobj_cb *cb)
-{
-	mutex_lock(&syncobj->cb_mutex);
-	list_del_init(&cb->node);
-	mutex_unlock(&syncobj->cb_mutex);
-}
+		ret = 0;
+	}
+	spin_unlock(&syncobj->lock);
 
-static void drm_syncobj_init(struct drm_syncobj *syncobj)
-{
-	spin_lock(&syncobj->pt_lock);
-	syncobj->timeline_context = dma_fence_context_alloc(1);
-	syncobj->timeline = 0;
-	syncobj->signal_point = 0;
-	init_waitqueue_head(&syncobj->wq);
-
-	INIT_LIST_HEAD(&syncobj->signal_pt_list);
-	spin_unlock(&syncobj->pt_lock);
+	return ret;
 }
 
-static void drm_syncobj_fini(struct drm_syncobj *syncobj)
+void drm_syncobj_add_callback(struct drm_syncobj *syncobj,
+			      struct drm_syncobj_cb *cb,
+			      drm_syncobj_func_t func)
 {
-	struct drm_syncobj_signal_pt *signal_pt = NULL, *tmp;
-
-	spin_lock(&syncobj->pt_lock);
-	list_for_each_entry_safe(signal_pt, tmp,
-				 &syncobj->signal_pt_list, list) {
-		list_del(&signal_pt->list);
-		dma_fence_put(&signal_pt->fence_array->base);
-		kfree(signal_pt);
-	}
-	spin_unlock(&syncobj->pt_lock);
+	spin_lock(&syncobj->lock);
+	drm_syncobj_add_callback_locked(syncobj, cb, func);
+	spin_unlock(&syncobj->lock);
 }
 
-static int drm_syncobj_create_signal_pt(struct drm_syncobj *syncobj,
-					struct dma_fence *fence,
-					u64 point)
+void drm_syncobj_remove_callback(struct drm_syncobj *syncobj,
+				 struct drm_syncobj_cb *cb)
 {
-	struct drm_syncobj_signal_pt *signal_pt =
-		kzalloc(sizeof(struct drm_syncobj_signal_pt), GFP_KERNEL);
-	struct drm_syncobj_signal_pt *tail_pt;
-	struct dma_fence **fences;
-	int num_fences = 0;
-	int ret = 0, i;
-
-	if (!signal_pt)
-		return -ENOMEM;
-	if (!fence)
-		goto out;
-
-	fences = kmalloc_array(sizeof(void *), 2, GFP_KERNEL);
-	if (!fences) {
-		ret = -ENOMEM;
-		goto out;
-	}
-	fences[num_fences++] = dma_fence_get(fence);
-	/* timeline syncobj must take this dependency */
-	if (syncobj->type == DRM_SYNCOBJ_TYPE_TIMELINE) {
-		spin_lock(&syncobj->pt_lock);
-		if (!list_empty(&syncobj->signal_pt_list)) {
-			tail_pt = list_last_entry(&syncobj->signal_pt_list,
-						  struct drm_syncobj_signal_pt, list);
-			fences[num_fences++] =
-				dma_fence_get(&tail_pt->fence_array->base);
-		}
-		spin_unlock(&syncobj->pt_lock);
-	}
-	signal_pt->fence_array = dma_fence_array_create(num_fences, fences,
-							syncobj->timeline_context,
-							point, false);
-	if (!signal_pt->fence_array) {
-		ret = -ENOMEM;
-		goto fail;
-	}
-
-	spin_lock(&syncobj->pt_lock);
-	if (syncobj->signal_point >= point) {
-		DRM_WARN("A later signal is ready!");
-		spin_unlock(&syncobj->pt_lock);
-		goto exist;
-	}
-	signal_pt->value = point;
-	list_add_tail(&signal_pt->list, &syncobj->signal_pt_list);
-	syncobj->signal_point = point;
-	spin_unlock(&syncobj->pt_lock);
-	wake_up_all(&syncobj->wq);
-
-	return 0;
-exist:
-	dma_fence_put(&signal_pt->fence_array->base);
-fail:
-	for (i = 0; i < num_fences; i++)
-		dma_fence_put(fences[i]);
-	kfree(fences);
-out:
-	kfree(signal_pt);
-	return ret;
+	spin_lock(&syncobj->lock);
+	list_del_init(&cb->node);
+	spin_unlock(&syncobj->lock);
 }
 
-static void drm_syncobj_garbage_collection(struct drm_syncobj *syncobj)
-{
-	struct drm_syncobj_signal_pt *signal_pt, *tmp, *tail_pt;
-
-	spin_lock(&syncobj->pt_lock);
-	tail_pt = list_last_entry(&syncobj->signal_pt_list,
-				  struct drm_syncobj_signal_pt,
-				  list);
-	list_for_each_entry_safe(signal_pt, tmp,
-				 &syncobj->signal_pt_list, list) {
-		if (syncobj->type == DRM_SYNCOBJ_TYPE_BINARY &&
-		    signal_pt == tail_pt)
-			continue;
-		if (dma_fence_is_signaled(&signal_pt->fence_array->base)) {
-			syncobj->timeline = signal_pt->value;
-			list_del(&signal_pt->list);
-			dma_fence_put(&signal_pt->fence_array->base);
-			kfree(signal_pt);
-		} else {
-			/*signal_pt is in order in list, from small to big, so
-			 * the later must not be signal either */
-			break;
-		}
-	}
-
-	spin_unlock(&syncobj->pt_lock);
-}
 /**
  * drm_syncobj_replace_fence - replace fence in a sync object.
  * @syncobj: Sync object to replace fence in
@@ -316,30 +165,28 @@ void drm_syncobj_replace_fence(struct drm_syncobj *syncobj,
 			       u64 point,
 			       struct dma_fence *fence)
 {
-	u64 pt_value = point;
-
-	drm_syncobj_garbage_collection(syncobj);
-	if (syncobj->type == DRM_SYNCOBJ_TYPE_BINARY) {
-		if (!fence) {
-			drm_syncobj_fini(syncobj);
-			drm_syncobj_init(syncobj);
-			return;
-		}
-		pt_value = syncobj->signal_point +
-			DRM_SYNCOBJ_BINARY_POINT;
-	}
-	drm_syncobj_create_signal_pt(syncobj, fence, pt_value);
-	if (fence) {
+	struct dma_fence *old_fence;
 	struct drm_syncobj_cb *cur, *tmp;
-		LIST_HEAD(cb_list);
 
-		mutex_lock(&syncobj->cb_mutex);
+	if (fence)
+		dma_fence_get(fence);
+
+	spin_lock(&syncobj->lock);
+
+	old_fence = rcu_dereference_protected(syncobj->fence,
+					      lockdep_is_held(&syncobj->lock));
+	rcu_assign_pointer(syncobj->fence, fence);
+
+	if (fence != old_fence) {
 		list_for_each_entry_safe(cur, tmp, &syncobj->cb_list, node) {
 			list_del_init(&cur->node);
 			cur->func(syncobj, cur);
 		}
-		mutex_unlock(&syncobj->cb_mutex);
 	}
+
+	spin_unlock(&syncobj->lock);
+
+	dma_fence_put(old_fence);
 }
 EXPORT_SYMBOL(drm_syncobj_replace_fence);
 
@@ -362,64 +209,6 @@ static int drm_syncobj_assign_null_handle(struct drm_syncobj *syncobj)
 	return 0;
 }
 
-static int
-drm_syncobj_point_get(struct drm_syncobj *syncobj, u64 point, u64 flags,
-		      struct dma_fence **fence)
-{
-	int ret = 0;
-
-	if (flags & DRM_SYNCOBJ_WAIT_FLAGS_WAIT_FOR_SUBMIT) {
-		ret = wait_event_interruptible(syncobj->wq,
-					       point <= syncobj->signal_point);
-		if (ret < 0)
-			return ret;
-	}
-	spin_lock(&syncobj->pt_lock);
-	*fence = drm_syncobj_find_signal_pt_for_point(syncobj, point);
-	if (!*fence)
-		ret = -EINVAL;
-	spin_unlock(&syncobj->pt_lock);
-	return ret;
-}
-
-/**
- * drm_syncobj_search_fence - lookup and reference the fence in a sync object or
- * in a timeline point
- * @syncobj: sync object pointer
- * @point: timeline point
- * @flags: DRM_SYNCOBJ_WAIT_FLAGS_WAIT_FOR_SUBMIT or not
- * @fence: out parameter for the fence
- *
- * if flags is DRM_SYNCOBJ_WAIT_FLAGS_WAIT_FOR_SUBMIT, the function will block
- * here until specific timeline points is reached.
- * if not, you need a submit thread and block in userspace until all future
- * timeline points have materialized, only then you can submit to the kernel,
- * otherwise, function will fail to return fence.
- *
- * Returns 0 on success or a negative error value on failure. On success @fence
- * contains a reference to the fence, which must be released by calling
- * dma_fence_put().
- */
-int drm_syncobj_search_fence(struct drm_syncobj *syncobj, u64 point,
-			     u64 flags, struct dma_fence **fence)
-{
-	u64 pt_value = point;
-
-	if (!syncobj)
-		return -ENOENT;
-
-	drm_syncobj_garbage_collection(syncobj);
-	if (syncobj->type == DRM_SYNCOBJ_TYPE_BINARY) {
-		/*BINARY syncobj always wait on last pt */
-		pt_value = syncobj->signal_point;
-
-		if (pt_value == 0)
-			pt_value += DRM_SYNCOBJ_BINARY_POINT;
-	}
-	return drm_syncobj_point_get(syncobj, pt_value, flags, fence);
-}
-EXPORT_SYMBOL(drm_syncobj_search_fence);
-
 /**
  * drm_syncobj_find_fence - lookup and reference the fence in a sync object
  * @file_private: drm file private pointer
@@ -429,7 +218,7 @@ EXPORT_SYMBOL(drm_syncobj_search_fence);
  * @fence: out parameter for the fence
  *
  * This is just a convenience function that combines drm_syncobj_find() and
- * drm_syncobj_lookup_fence().
+ * drm_syncobj_fence_get().
  *
  * Returns 0 on success or a negative error value on failure. On success @fence
  * contains a reference to the fence, which must be released by calling
@@ -440,10 +229,15 @@ int drm_syncobj_find_fence(struct drm_file *file_private,
 			   struct dma_fence **fence)
 {
 	struct drm_syncobj *syncobj = drm_syncobj_find(file_private, handle);
-	int ret;
+	int ret = 0;
 
-	ret = drm_syncobj_search_fence(syncobj, point, flags, fence);
-	if (syncobj)
+	if (!syncobj)
+		return -ENOENT;
+
+	*fence = drm_syncobj_fence_get(syncobj);
+	if (!*fence) {
+		ret = -EINVAL;
+	}
 	drm_syncobj_put(syncobj);
 	return ret;
 }
@@ -460,7 +254,7 @@ void drm_syncobj_free(struct kref *kref)
 	struct drm_syncobj *syncobj = container_of(kref,
 						   struct drm_syncobj,
 						   refcount);
-	drm_syncobj_fini(syncobj);
+	drm_syncobj_replace_fence(syncobj, 0, NULL);
 	kfree(syncobj);
 }
 EXPORT_SYMBOL(drm_syncobj_free);
@@ -493,13 +287,7 @@ int drm_syncobj_create(struct drm_syncobj **out_syncobj, uint32_t flags,
 
 	kref_init(&syncobj->refcount);
 	INIT_LIST_HEAD(&syncobj->cb_list);
-	spin_lock_init(&syncobj->pt_lock);
-	mutex_init(&syncobj->cb_mutex);
-	if (flags & DRM_SYNCOBJ_CREATE_TYPE_TIMELINE)
-		syncobj->type = DRM_SYNCOBJ_TYPE_TIMELINE;
-	else
-		syncobj->type = DRM_SYNCOBJ_TYPE_BINARY;
-	drm_syncobj_init(syncobj);
+	spin_lock_init(&syncobj->lock);
 
 	if (flags & DRM_SYNCOBJ_CREATE_SIGNALED) {
 		ret = drm_syncobj_assign_null_handle(syncobj);
@@ -782,8 +570,7 @@ drm_syncobj_create_ioctl(struct drm_device *dev, void *data,
 		return -EOPNOTSUPP;
 
 	/* no valid flags yet */
-	if (args->flags & ~(DRM_SYNCOBJ_CREATE_SIGNALED |
-			    DRM_SYNCOBJ_CREATE_TYPE_TIMELINE))
+	if (args->flags & ~DRM_SYNCOBJ_CREATE_SIGNALED)
 		return -EINVAL;
 
 	return drm_syncobj_create_as_handle(file_private,
@@ -876,8 +663,9 @@ static void syncobj_wait_syncobj_func(struct drm_syncobj *syncobj,
 	struct syncobj_wait_entry *wait =
 		container_of(cb, struct syncobj_wait_entry, syncobj_cb);
 
-	drm_syncobj_search_fence(syncobj, 0, 0, &wait->fence);
-
+	/* This happens inside the syncobj lock */
+	wait->fence = dma_fence_get(rcu_dereference_protected(syncobj->fence,
+							      lockdep_is_held(&syncobj->lock)));
 	wake_up_process(wait->task);
 }
 
@@ -903,8 +691,7 @@ static signed long drm_syncobj_array_wait_timeout(struct drm_syncobj **syncobjs,
 	signaled_count = 0;
 	for (i = 0; i < count; ++i) {
 		entries[i].task = current;
-		drm_syncobj_search_fence(syncobjs[i], 0, 0,
-					 &entries[i].fence);
+		entries[i].fence = drm_syncobj_fence_get(syncobjs[i]);
 		if (!entries[i].fence) {
 			if (flags & DRM_SYNCOBJ_WAIT_FLAGS_WAIT_FOR_SUBMIT) {
 				continue;
@@ -935,9 +722,6 @@ static signed long drm_syncobj_array_wait_timeout(struct drm_syncobj **syncobjs,
 
 	if (flags & DRM_SYNCOBJ_WAIT_FLAGS_WAIT_FOR_SUBMIT) {
 		for (i = 0; i < count; ++i) {
-			if (entries[i].fence)
-				continue;
-
 			drm_syncobj_fence_get_or_add_callback(syncobjs[i],
 							      &entries[i].fence,
 							      &entries[i].syncobj_cb,
@@ -1169,13 +953,12 @@ drm_syncobj_reset_ioctl(struct drm_device *dev, void *data,
 	if (ret < 0)
 		return ret;
 
-	for (i = 0; i < args->count_handles; i++) {
-		drm_syncobj_fini(syncobjs[i]);
-		drm_syncobj_init(syncobjs[i]);
-	}
+	for (i = 0; i < args->count_handles; i++)
+		drm_syncobj_replace_fence(syncobjs[i], 0, NULL);
+
 	drm_syncobj_array_free(syncobjs, args->count_handles);
 
-	return ret;
+	return 0;
 }
 
 int

include/drm/drm_syncobj.h

@@ -30,18 +30,10 @@
 
 struct drm_syncobj_cb;
 
-/* Move the define here for the moment to avoid exposing the UAPI just yet */
-#define DRM_SYNCOBJ_CREATE_TYPE_TIMELINE (1 << 1)
-
-enum drm_syncobj_type {
-	DRM_SYNCOBJ_TYPE_BINARY,
-	DRM_SYNCOBJ_TYPE_TIMELINE
-};
-
 /**
  * struct drm_syncobj - sync object.
  *
- * This structure defines a generic sync object which is timeline based.
+ * This structure defines a generic sync object which wraps a &dma_fence.
  */
 struct drm_syncobj {
 	/**
@@ -49,42 +41,21 @@ struct drm_syncobj {
 	 */
 	struct kref refcount;
 	/**
-	 * @type: indicate syncobj type
-	 */
-	enum drm_syncobj_type type;
-	/**
-	 * @wq: wait signal operation work queue
-	 */
-	wait_queue_head_t	wq;
-	/**
-	 * @timeline_context: fence context used by timeline
-	 */
-	u64 timeline_context;
-	/**
-	 * @timeline: syncobj timeline value, which indicates point is signaled.
-	 */
-	u64 timeline;
-	/**
-	 * @signal_point: which indicates the latest signaler point.
+	 * @fence:
+	 * NULL or a pointer to the fence bound to this object.
+	 *
+	 * This field should not be used directly. Use drm_syncobj_fence_get()
+	 * and drm_syncobj_replace_fence() instead.
 	 */
-	u64 signal_point;
-	/**
-	 * @signal_pt_list: signaler point list.
-	 */
-	struct list_head signal_pt_list;
-
+	struct dma_fence __rcu *fence;
 	/**
 	 * @cb_list: List of callbacks to call when the &fence gets replaced.
 	 */
 	struct list_head cb_list;
 	/**
-	 * @pt_lock: Protects pt list.
-	 */
-	spinlock_t pt_lock;
-	/**
-	 * @cb_mutex: Protects syncobj cb list.
+	 * @lock: Protects &cb_list and write-locks &fence.
 	 */
-	struct mutex cb_mutex;
+	spinlock_t lock;
 	/**
 	 * @file: A file backing for this syncobj.
 	 */
@@ -135,6 +106,29 @@ drm_syncobj_put(struct drm_syncobj *obj)
 	kref_put(&obj->refcount, drm_syncobj_free);
 }
 
+/**
+ * drm_syncobj_fence_get - get a reference to a fence in a sync object
+ * @syncobj: sync object.
+ *
+ * This acquires additional reference to &drm_syncobj.fence contained in @obj,
+ * if not NULL. It is illegal to call this without already holding a reference.
+ * No locks required.
+ *
+ * Returns:
+ * Either the fence of @obj or NULL if there's none.
+ */
+static inline struct dma_fence *
+drm_syncobj_fence_get(struct drm_syncobj *syncobj)
+{
+	struct dma_fence *fence;
+
+	rcu_read_lock();
+	fence = dma_fence_get_rcu_safe(&syncobj->fence);
+	rcu_read_unlock();
+
+	return fence;
+}
+
 struct drm_syncobj *drm_syncobj_find(struct drm_file *file_private,
 				     u32 handle);
 void drm_syncobj_replace_fence(struct drm_syncobj *syncobj, u64 point,
@@ -148,7 +142,5 @@ int drm_syncobj_create(struct drm_syncobj **out_syncobj, uint32_t flags,
 int drm_syncobj_get_handle(struct drm_file *file_private,
 			   struct drm_syncobj *syncobj, u32 *handle);
 int drm_syncobj_get_fd(struct drm_syncobj *syncobj, int *p_fd);
-int drm_syncobj_search_fence(struct drm_syncobj *syncobj, u64 point, u64 flags,
-			     struct dma_fence **fence);
 
 #endif