Re: [PATCH 2/2] drm: Revert syncobj timeline changes.

["Koenig, Christian" <Christian.Koenig@amd.com>]

Am 08.11.18 um 17:04 schrieb Eric Anholt:
> Daniel suggested I submit this, since we're still seeing regressions
> from it.  This is a revert to before 48197bc564c7 ("drm: add syncobj
> timeline support v9") and its followon fixes.

This is a harmless false positive from lockdep, Chouming and I are 
already working on a fix.

Christian.

>
> 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>
> ---
>   drivers/gpu/drm/drm_syncobj.c | 359 +++++++---------------------------
>   include/drm/drm_syncobj.h     |  73 ++++---
>   2 files changed, 105 insertions(+), 327 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c
> index da8175d9c6ff..e2c5b3ca4824 100644
> --- a/drivers/gpu/drm/drm_syncobj.c
> +++ b/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,
> -						  struct dma_fence **fence,
> -						  struct drm_syncobj_cb *cb,
> -						  drm_syncobj_func_t func)
> +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 drm_syncobj_cb *cur, *tmp;
> -		LIST_HEAD(cb_list);
> +	struct dma_fence *old_fence;
> +	struct drm_syncobj_cb *cur, *tmp;
> +
> +	if (fence)
> +		dma_fence_get(fence);
> +
> +	spin_lock(&syncobj->lock);
>   
> -		mutex_lock(&syncobj->cb_mutex);
> +	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
> @@ -440,11 +229,16 @@ 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)
> -		drm_syncobj_put(syncobj);
> +	if (!syncobj)
> +		return -ENOENT;
> +
> +	*fence = drm_syncobj_fence_get(syncobj);
> +	if (!*fence) {
> +		ret = -EINVAL;
> +	}
> +	drm_syncobj_put(syncobj);
>   	return ret;
>   }
>   EXPORT_SYMBOL(drm_syncobj_find_fence);
> @@ -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);
> @@ -489,13 +283,7 @@ 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);
> @@ -778,8 +566,7 @@ 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,
> @@ -872,8 +659,9 @@ 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);
>   }
>   
> @@ -899,8 +687,7 @@ 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;
> @@ -931,9 +718,6 @@ 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,
> @@ -1165,13 +949,12 @@ 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
> diff --git a/include/drm/drm_syncobj.h b/include/drm/drm_syncobj.h
> index 29244cbcd05e..2eda44def639 100644
> --- a/include/drm/drm_syncobj.h
> +++ b/include/drm/drm_syncobj.h
> @@ -30,15 +30,10 @@
>   
>   struct drm_syncobj_cb;
>   
> -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 {
>   	/**
> @@ -46,42 +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
> +	 * @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 timeline_context;
> +	struct dma_fence __rcu *fence;
>   	/**
> -	 * @timeline: syncobj timeline value, which indicates point is signaled.
> +	 * @cb_list: List of callbacks to call when the &fence gets replaced.
>   	 */
> -	u64 timeline;
> -	/**
> -	 * @signal_point: which indicates the latest signaler point.
> -	 */
> -	u64 signal_point;
> -	/**
> -	 * @signal_pt_list: signaler point list.
> -	 */
> -	struct list_head signal_pt_list;
> -
> -	/**
> -         * @cb_list: List of callbacks to call when the &fence gets replaced.
> -         */
>   	struct list_head cb_list;
>   	/**
> -	 * @pt_lock: Protects pt list.
> +	 * @lock: Protects &cb_list and write-locks &fence.
>   	 */
> -	spinlock_t pt_lock;
> -	/**
> -	 * @cb_mutex: Protects syncobj cb list.
> -	 */
> -	struct mutex cb_mutex;
> +	spinlock_t lock;
>   	/**
>   	 * @file: A file backing for this syncobj.
>   	 */
> @@ -94,7 +68,7 @@ typedef void (*drm_syncobj_func_t)(struct drm_syncobj *syncobj,
>   /**
>    * struct drm_syncobj_cb - callback for drm_syncobj_add_callback
>    * @node: used by drm_syncob_add_callback to append this struct to
> - *       &drm_syncobj.cb_list
> + *	  &drm_syncobj.cb_list
>    * @func: drm_syncobj_func_t to call
>    *
>    * This struct will be initialized by drm_syncobj_add_callback, additional
> @@ -132,6 +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,
> @@ -145,7 +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