Am 22.10.24 um 18:18 schrieb Chia-I Wu:
Userspace might poll a syncobj with the query ioctl. Call
dma_fence_enable_sw_signaling to ensure dma_fence_is_signaled returns
true in finite time.
Wait a second, just querying the fence status is absolutely not
guaranteed to return true in finite time. That is well documented on the
dma_fence() object.
When you want to poll on signaling from userspace you really need to
call poll or the wait IOCTL with a zero timeout. That will also return
immediately but should enable signaling while doing that.
So just querying the status should absolutely *not* enable signaling.
That's an intentional separation.
Regards,
Christian.
Fixes: 27b575a9aa2f ("drm/syncobj: add timeline payload query ioctl v6")
Signed-off-by: Chia-I Wu <olvaffe@xxxxxxxxx>
---
v2: add Signed-off-by and Fixes tags
---
drivers/gpu/drm/drm_syncobj.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c
index 4fcfc0b9b386c..58c5593c897a2 100644
--- a/drivers/gpu/drm/drm_syncobj.c
+++ b/drivers/gpu/drm/drm_syncobj.c
@@ -1689,6 +1689,9 @@ int drm_syncobj_query_ioctl(struct drm_device *dev, void *data,
DRM_SYNCOBJ_QUERY_FLAGS_LAST_SUBMITTED) {
point = fence->seqno;
} else {
+ /* ensure forward progress */
+ dma_fence_enable_sw_signaling(fence);
+
dma_fence_chain_for_each(iter, fence) {
if (iter->context != fence->context) {
dma_fence_put(iter);
