Am 12.04.2017 um 12:18 schrieb Chris Wilson:
On Wed, Apr 12, 2017 at 11:55:24AM +0200, Christian König wrote:
Am 12.04.2017 um 06:57 schrieb Dave Airlie:
+static int amdgpu_sem_lookup_and_remove(struct amdgpu_cs_parser *p,
+ uint32_t handle)
+{
+ int r;
+ struct dma_fence *old_fence;
+
+ r = drm_syncobj_replace_fence(p->filp, handle, NULL);
+ if (r)
+ return r;
+ dma_fence_put(old_fence);
Am I wrong or is old_fence not initialized here?
Additional to that what happens when the fence in the sync object
was changed while we do the CS? Or even worse the handle got
assigned to a new sync object.
We either ww_mutex the lot, or regard that as a userspace race where the
order between the two concurrent CS emits is undefined and who gets the
in-semaphore is happenstance.
My thinking to solve this was rather a) resolve the handle to an object
only once and b) replace the old fence with NULL only if it didn't changed.
Letting userspace race here is also an option, but I would prefer it
another solution.
Christian.
-Chris
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