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Reply-To: christian.koenig@amd.com
Subject: Re: [PATCH 2/2] drm: Revert syncobj timeline changes.
To:     "Koenig, Christian" <Christian.Koenig@amd.com>,
        Eric Anholt <eric@anholt.net>,
        "dri-devel@lists.freedesktop.org" <dri-devel@lists.freedesktop.org>
Cc:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Daniel Vetter <daniel.vetter@ffwll.ch>
References: <20181108160422.17743-1-eric@anholt.net>
 <20181108160422.17743-3-eric@anholt.net>
 <635caa27-eb0b-a4d6-5a1d-3fbe5382bd6b@amd.com>
From:   =?UTF-8?Q?Christian_K=c3=b6nig?= <ckoenig.leichtzumerken@gmail.com>
Message-ID: <c5af6df2-d5d5-5276-3628-4bac0fd53c98@gmail.com>
Date:   Thu, 8 Nov 2018 17:52:56 +0100
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Am 08.11.18 um 17:07 schrieb Koenig, Christian:
> 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.

On the other hand we had enough trouble with that patch, so if it really 
bothers you feel free to add my Acked-by: Christian König 
<christian.koenig@amd.com> and push it.

Christian.

>
> 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
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