drm/syncobj: use newly allocated stub fences

Allocate a new private stub fence in drm_syncobj_assign_null_handle,
instead of using a static stub fence.

When userspace creates a fence with DRM_SYNCOBJ_CREATE_SIGNALED or when
userspace signals a fence via DRM_IOCTL_SYNCOBJ_SIGNAL, the timestamp
obtained when the fence is exported and queried with SYNC_IOC_FILE_INFO
should match when the fence's status was changed from the perspective of
userspace, which is during the respective ioctl.

When a static stub fence started being used in by these ioctls, this
behavior changed. Instead, the timestamp returned by SYNC_IOC_FILE_INFO
became the first time anything used the static stub fence, which has no
meaning to userspace.

Signed-off-by: David Stevens <stevensd@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20210408095428.3983055-1-stevensd@google.com
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Christian König <christian.koenig@amd.com>

diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c
index d64fc03..ce0f5ef 100644 (file)
--- a/drivers/dma-buf/dma-fence.c
+++ b/drivers/dma-buf/dma-fence.c
@@ -123,7 +123,9 @@ static const struct dma_fence_ops dma_fence_stub_ops = {
 /**
  * dma_fence_get_stub - return a signaled fence
  *
- * Return a stub fence which is already signaled.
+ * Return a stub fence which is already signaled. The fence's
+ * timestamp corresponds to the first time after boot this
+ * function is called.
  */
 struct dma_fence *dma_fence_get_stub(void)
 {
@@ -142,6 +144,29 @@ struct dma_fence *dma_fence_get_stub(void)
 EXPORT_SYMBOL(dma_fence_get_stub);
 
 /**
+ * dma_fence_allocate_private_stub - return a private, signaled fence
+ *
+ * Return a newly allocated and signaled stub fence.
+ */
+struct dma_fence *dma_fence_allocate_private_stub(void)
+{
+       struct dma_fence *fence;
+
+       fence = kzalloc(sizeof(*fence), GFP_KERNEL);
+       if (fence == NULL)
+               return ERR_PTR(-ENOMEM);
+
+       dma_fence_init(fence,
+                      &dma_fence_stub_ops,
+                      &dma_fence_stub_lock,
+                      0, 0);
+       dma_fence_signal(fence);
+
+       return fence;
+}
+EXPORT_SYMBOL(dma_fence_allocate_private_stub);
+
+/**
  * dma_fence_context_alloc - allocate an array of fence contexts
  * @num: amount of contexts to allocate
  *

diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c
index 6231a82..fdd2ec8 100644 (file)
--- a/drivers/gpu/drm/drm_syncobj.c
+++ b/drivers/gpu/drm/drm_syncobj.c
@@ -350,12 +350,16 @@ EXPORT_SYMBOL(drm_syncobj_replace_fence);
  *
  * Assign a already signaled stub fence to the sync object.
  */
-static void drm_syncobj_assign_null_handle(struct drm_syncobj *syncobj)
+static int drm_syncobj_assign_null_handle(struct drm_syncobj *syncobj)
 {
-       struct dma_fence *fence = dma_fence_get_stub();
+       struct dma_fence *fence = dma_fence_allocate_private_stub();
+
+       if (IS_ERR(fence))
+               return PTR_ERR(fence);
 
        drm_syncobj_replace_fence(syncobj, fence);
        dma_fence_put(fence);
+       return 0;
 }
 
 /* 5s default for wait submission */
@@ -478,6 +482,7 @@ EXPORT_SYMBOL(drm_syncobj_free);
 int drm_syncobj_create(struct drm_syncobj **out_syncobj, uint32_t flags,
                       struct dma_fence *fence)
 {
+       int ret;
        struct drm_syncobj *syncobj;
 
        syncobj = kzalloc(sizeof(struct drm_syncobj), GFP_KERNEL);
@@ -488,8 +493,13 @@ int drm_syncobj_create(struct drm_syncobj **out_syncobj, uint32_t flags,
        INIT_LIST_HEAD(&syncobj->cb_list);
        spin_lock_init(&syncobj->lock);
 
-       if (flags & DRM_SYNCOBJ_CREATE_SIGNALED)
-               drm_syncobj_assign_null_handle(syncobj);
+       if (flags & DRM_SYNCOBJ_CREATE_SIGNALED) {
+               ret = drm_syncobj_assign_null_handle(syncobj);
+               if (ret < 0) {
+                       drm_syncobj_put(syncobj);
+                       return ret;
+               }
+       }
 
        if (fence)
                drm_syncobj_replace_fence(syncobj, fence);
@@ -1334,8 +1344,11 @@ drm_syncobj_signal_ioctl(struct drm_device *dev, void *data,
        if (ret < 0)
                return ret;
 
-       for (i = 0; i < args->count_handles; i++)
-               drm_syncobj_assign_null_handle(syncobjs[i]);
+       for (i = 0; i < args->count_handles; i++) {
+               ret = drm_syncobj_assign_null_handle(syncobjs[i]);
+               if (ret < 0)
+                       break;
+       }
 
        drm_syncobj_array_free(syncobjs, args->count_handles);
 

diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h
index 9f12efa..6ffb4b2 100644 (file)
--- a/include/linux/dma-fence.h
+++ b/include/linux/dma-fence.h
@@ -587,6 +587,7 @@ static inline signed long dma_fence_wait(struct dma_fence *fence, bool intr)
 }
 
 struct dma_fence *dma_fence_get_stub(void);
+struct dma_fence *dma_fence_allocate_private_stub(void);
 u64 dma_fence_context_alloc(unsigned num);
 
 #define DMA_FENCE_TRACE(f, fmt, args...) \