dma-buf: add dma_fence_timestamp helper

When a fence signals there is a very small race window where the timestamp
isn't updated yet. sync_file solves this by busy waiting for the
timestamp to appear, but on other ocassions didn't handled this
correctly.

Provide a dma_fence_timestamp() helper function for this and use it in
all appropriate cases.

Another alternative would be to grab the spinlock when that happens.

v2 by teddy: add a wait parameter to wait for the timestamp to show up, in case
   the accurate timestamp is needed and/or the timestamp is not based on
   ktime (e.g. hw timestamp)
v3 chk: drop the parameter again for unified handling

Signed-off-by: Yunxiang Li <Yunxiang.Li@amd.com>
Signed-off-by: Christian König <christian.koenig@amd.com>
Fixes: 1774baa64f93 ("drm/scheduler: Change scheduled fence track v2")
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
CC: stable@vger.kernel.org
Link: https://patchwork.freedesktop.org/patch/msgid/20230929104725.2358-1-christian.koenig@amd.com

diff --git a/drivers/dma-buf/dma-fence-unwrap.c b/drivers/dma-buf/dma-fence-unwrap.c
index c625bb2..628af51 100644 (file)
--- a/drivers/dma-buf/dma-fence-unwrap.c
+++ b/drivers/dma-buf/dma-fence-unwrap.c
@@ -76,16 +76,11 @@ struct dma_fence *__dma_fence_unwrap_merge(unsigned int num_fences,
                dma_fence_unwrap_for_each(tmp, &iter[i], fences[i]) {
                        if (!dma_fence_is_signaled(tmp)) {
                                ++count;
-                       } else if (test_bit(DMA_FENCE_FLAG_TIMESTAMP_BIT,
-                                           &tmp->flags)) {
-                               if (ktime_after(tmp->timestamp, timestamp))
-                                       timestamp = tmp->timestamp;
                        } else {
-                               /*
-                                * Use the current time if the fence is
-                                * currently signaling.
-                                */
-                               timestamp = ktime_get();
+                               ktime_t t = dma_fence_timestamp(tmp);
+
+                               if (ktime_after(t, timestamp))
+                                       timestamp = t;
                        }
                }
        }

diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c
index af57799..2e9a316 100644 (file)
--- a/drivers/dma-buf/sync_file.c
+++ b/drivers/dma-buf/sync_file.c
@@ -268,13 +268,10 @@ static int sync_fill_fence_info(struct dma_fence *fence,
                sizeof(info->driver_name));
 
        info->status = dma_fence_get_status(fence);
-       while (test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags) &&
-              !test_bit(DMA_FENCE_FLAG_TIMESTAMP_BIT, &fence->flags))
-               cpu_relax();
        info->timestamp_ns =
-               test_bit(DMA_FENCE_FLAG_TIMESTAMP_BIT, &fence->flags) ?
-               ktime_to_ns(fence->timestamp) :
-               ktime_set(0, 0);
+               dma_fence_is_signaled(fence) ?
+                       ktime_to_ns(dma_fence_timestamp(fence)) :
+                       ktime_set(0, 0);
 
        return info->status;
 }

diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c
index 506371c..5a3a622 100644 (file)
--- a/drivers/gpu/drm/scheduler/sched_main.c
+++ b/drivers/gpu/drm/scheduler/sched_main.c
@@ -929,7 +929,7 @@ drm_sched_get_cleanup_job(struct drm_gpu_scheduler *sched)
 
                if (next) {
                        next->s_fence->scheduled.timestamp =
-                               job->s_fence->finished.timestamp;
+                               dma_fence_timestamp(&job->s_fence->finished);
                        /* start TO timer for next job */
                        drm_sched_start_timeout(sched);
                }

diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h
index 0d678e9..ebe78bd 100644 (file)
--- a/include/linux/dma-fence.h
+++ b/include/linux/dma-fence.h
@@ -568,6 +568,25 @@ static inline void dma_fence_set_error(struct dma_fence *fence,
        fence->error = error;
 }
 
+/**
+ * dma_fence_timestamp - helper to get the completion timestamp of a fence
+ * @fence: fence to get the timestamp from.
+ *
+ * After a fence is signaled the timestamp is updated with the signaling time,
+ * but setting the timestamp can race with tasks waiting for the signaling. This
+ * helper busy waits for the correct timestamp to appear.
+ */
+static inline ktime_t dma_fence_timestamp(struct dma_fence *fence)
+{
+       if (WARN_ON(!test_bit(DMA_FENCE_FLAG_SIGNALED_BIT, &fence->flags)))
+               return ktime_get();
+
+       while (!test_bit(DMA_FENCE_FLAG_TIMESTAMP_BIT, &fence->flags))
+               cpu_relax();
+
+       return fence->timestamp;
+}
+
 signed long dma_fence_wait_timeout(struct dma_fence *,
                                   bool intr, signed long timeout);
 signed long dma_fence_wait_any_timeout(struct dma_fence **fences,