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Subject: Re: [PATCH 2/2] drm: Revert syncobj timeline changes.
To:     <christian.koenig@amd.com>, Eric Anholt <eric@anholt.net>,
        "dri-devel@lists.freedesktop.org" <dri-devel@lists.freedesktop.org>
CC:     Daniel Vetter <daniel.vetter@ffwll.ch>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
References: <20181108160422.17743-1-eric@anholt.net>
 <20181108160422.17743-3-eric@anholt.net>
 <635caa27-eb0b-a4d6-5a1d-3fbe5382bd6b@amd.com>
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Date:   Fri, 9 Nov 2018 10:35:27 +0800
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On 2018年11月09日 00:52, Christian König wrote:
> 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.
NAK, please no, I don't think this needed, the Warning totally isn't 
related to syncobj timeline, but fence-array implementation flaw, just 
exposed by syncobj.
In addition, Christian already has a fix for this Warning, I've tested. 
Please Christian send to public review.

-David
>
> 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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