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






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@xxxxxxx> 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@xxxxxxx>
Cc: Christian König <christian.koenig@xxxxxxx>
Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
Signed-off-by: Eric Anholt <eric@xxxxxxxxxx>
---
   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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