FAILED: patch "[PATCH] dma-buf: add dma_fence_timestamp helper" failed to apply to 5.15-stable tree

The patch below does not apply to the 5.15-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x b83ce9cb4a465b8f9a3fa45561b721a9551f60e3
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2023101522-oven-reformat-207c@gregkh' --subject-prefix 'PATCH 5.15.y' HEAD^..

Possible dependencies:

b83ce9cb4a46 ("dma-buf: add dma_fence_timestamp helper")
f781f661e8c9 ("dma-buf: keep the signaling time of merged fences v3") bafaf67c42f4 ("Revert "drm/sched: Use parent fence instead of finished"") e4dc45b1848b ("drm/sched: Use parent fence instead of finished")
c85d00d4fd8b ("dma-buf: set signaling bit for the stub fence")
bbd60fee2d21 ("dma-buf: revert "return only unsignaled fences in dma_fence_unwrap_for_each v3"") 245a4a7b531c ("dma-buf: generalize dma_fence unwrap & merging v3")
01357a5a45ed ("dma-buf: cleanup dma_fence_unwrap implementation")
f778f405faa2 ("dma-buf/sync_file: cleanup fence merging a bit")
21d139d73f77 ("dma-buf/sync-file: fix logic error in new fence merge code") 519f490db07e ("dma-buf/sync-file: fix warning about fence containers") 64a8f92fd783 ("dma-buf: add dma_fence_unwrap v2")
caaf2ae712b7 ("dma-buf: Add dma_fence_array_for_each (v2)")
1d51775cd3f5 ("dma-buf: add dma_resv selftest v4")
bcf26654a38f ("drm/sched: fix the bug of time out calculation(v4)")
992c238188a8 ("dma-buf: nuke seqno-fence")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From b83ce9cb4a465b8f9a3fa45561b721a9551f60e3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Christian=20K=C3=B6nig?= <[email protected]>
Date: Fri, 8 Sep 2023 10:27:23 +0200
Subject: [PATCH] dma-buf: add dma_fence_timestamp helper
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

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

index c625bb2b5d56..628af51c81af 100644
@@ -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;
 			}
 		}
 	}

index af57799c86ce..2e9a316c596a 100644
@@ -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;
 }

index 506371c42745..5a3a622fc672 100644
@@ -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);
 		}

index 0d678e9a7b24..ebe78bd3d121 100644
@@ -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,