[PATCH 6.1 116/131] dma-buf: add dma_fence_timestamp helper

Greg Kroah-Hartman
2023-10-16T09:04:17Z

From: Christian König <christian.koenig@amd.com>

commit b83ce9cb4a465b8f9a3fa45561b721a9551f60e3 upstream.

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
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/dma-buf/dma-fence-unwrap.c | 13 ++++---------
drivers/dma-buf/sync_file.c | 9 +++------
drivers/gpu/drm/scheduler/sched_main.c | 2 +-
include/linux/dma-fence.h | 19 +++++++++++++++++++
4 files changed, 27 insertions(+), 16 deletions(-)

--- 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_mer
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;
}
}
}
--- 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 d
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;
}
--- a/drivers/gpu/drm/scheduler/sched_main.c
+++ b/drivers/gpu/drm/scheduler/sched_main.c
@@ -841,7 +841,7 @@ drm_sched_get_cleanup_job(struct drm_gpu

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);
}
--- a/include/linux/dma-fence.h
+++ b/include/linux/dma-fence.h
@@ -548,6 +548,25 @@ static inline void dma_fence_set_error(s
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,