5.15-stable review patch. If anyone has any objections, please let me know.
------------------
From: Christian König <christian.koenig@xxxxxxx>
[ Upstream commit b83ce9cb4a465b8f9a3fa45561b721a9551f60e3 ]
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@xxxxxxx>
Signed-off-by: Christian König <christian.koenig@xxxxxxx>
Fixes: 1774baa64f93 ("drm/scheduler: Change scheduled fence track v2")
Reviewed-by: Alex Deucher <alexander.deucher@xxxxxxx>
CC: stable@xxxxxxxxxxxxxxx
Link: https://patchwork.freedesktop.org/patch/msgid/20230929104725.2358-1-christian.koenig@xxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
drivers/dma-buf/dma-fence-unwrap.c | 176 +++++++++++++++++++++++++
drivers/dma-buf/sync_file.c | 9 +-
drivers/gpu/drm/scheduler/sched_main.c | 3 +-
include/linux/dma-fence.h | 19 +++
4 files changed, 199 insertions(+), 8 deletions(-)
create mode 100644 drivers/dma-buf/dma-fence-unwrap.c
diff --git a/drivers/dma-buf/dma-fence-unwrap.c b/drivers/dma-buf/dma-fence-unwrap.c
new file mode 100644
index 000000000000..628af51c81af
--- /dev/null
+++ b/drivers/dma-buf/dma-fence-unwrap.c
@@ -0,0 +1,176 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * dma-fence-util: misc functions for dma_fence objects
+ *
+ * Copyright (C) 2022 Advanced Micro Devices, Inc.
+ * Authors:
+ * Christian König <christian.koenig@xxxxxxx>
+ */
+
+#include <linux/dma-fence.h>
+#include <linux/dma-fence-array.h>
+#include <linux/dma-fence-chain.h>
+#include <linux/dma-fence-unwrap.h>
+#include <linux/slab.h>
+
+/* Internal helper to start new array iteration, don't use directly */
+static struct dma_fence *
+__dma_fence_unwrap_array(struct dma_fence_unwrap *cursor)
+{
+ cursor->array = dma_fence_chain_contained(cursor->chain);
+ cursor->index = 0;
+ return dma_fence_array_first(cursor->array);
+}
+
+/**
+ * dma_fence_unwrap_first - return the first fence from fence containers
+ * @head: the entrypoint into the containers
+ * @cursor: current position inside the containers
+ *
+ * Unwraps potential dma_fence_chain/dma_fence_array containers and return the
+ * first fence.
+ */
+struct dma_fence *dma_fence_unwrap_first(struct dma_fence *head,
+ struct dma_fence_unwrap *cursor)
+{
+ cursor->chain = dma_fence_get(head);
+ return __dma_fence_unwrap_array(cursor);
+}
+EXPORT_SYMBOL_GPL(dma_fence_unwrap_first);
+
+/**
+ * dma_fence_unwrap_next - return the next fence from a fence containers
+ * @cursor: current position inside the containers
+ *
+ * Continue unwrapping the dma_fence_chain/dma_fence_array containers and return
+ * the next fence from them.
+ */
+struct dma_fence *dma_fence_unwrap_next(struct dma_fence_unwrap *cursor)
+{
+ struct dma_fence *tmp;
+
+ ++cursor->index;
+ tmp = dma_fence_array_next(cursor->array, cursor->index);
+ if (tmp)
+ return tmp;
+
+ cursor->chain = dma_fence_chain_walk(cursor->chain);
+ return __dma_fence_unwrap_array(cursor);
+}
+EXPORT_SYMBOL_GPL(dma_fence_unwrap_next);
+
+/* Implementation for the dma_fence_merge() marco, don't use directly */
+struct dma_fence *__dma_fence_unwrap_merge(unsigned int num_fences,
+ struct dma_fence **fences,
+ struct dma_fence_unwrap *iter)
+{
+ struct dma_fence_array *result;
+ struct dma_fence *tmp, **array;
+ ktime_t timestamp;
+ unsigned int i;
+ size_t count;
+
+ count = 0;
+ timestamp = ns_to_ktime(0);
+ for (i = 0; i < num_fences; ++i) {
+ dma_fence_unwrap_for_each(tmp, &iter[i], fences[i]) {
+ if (!dma_fence_is_signaled(tmp)) {
+ ++count;
+ } else {
+ ktime_t t = dma_fence_timestamp(tmp);
+
+ if (ktime_after(t, timestamp))
+ timestamp = t;
+ }
+ }
+ }
+
+ /*
+ * If we couldn't find a pending fence just return a private signaled
+ * fence with the timestamp of the last signaled one.
+ */
+ if (count == 0)
+ return dma_fence_allocate_private_stub(timestamp);
+
+ array = kmalloc_array(count, sizeof(*array), GFP_KERNEL);
+ if (!array)
+ return NULL;
+
+ /*
+ * This trashes the input fence array and uses it as position for the
+ * following merge loop. This works because the dma_fence_merge()
+ * wrapper macro is creating this temporary array on the stack together
+ * with the iterators.
+ */
+ for (i = 0; i < num_fences; ++i)
+ fences[i] = dma_fence_unwrap_first(fences[i], &iter[i]);
+
+ count = 0;
+ do {
+ unsigned int sel;
+
+restart:
+ tmp = NULL;
+ for (i = 0; i < num_fences; ++i) {
+ struct dma_fence *next;
+
+ while (fences[i] && dma_fence_is_signaled(fences[i]))
+ fences[i] = dma_fence_unwrap_next(&iter[i]);
+
+ next = fences[i];
+ if (!next)
+ continue;
+
+ /*
+ * We can't guarantee that inpute fences are ordered by
+ * context, but it is still quite likely when this
+ * function is used multiple times. So attempt to order
+ * the fences by context as we pass over them and merge
+ * fences with the same context.
+ */
+ if (!tmp || tmp->context > next->context) {
+ tmp = next;
+ sel = i;
+
+ } else if (tmp->context < next->context) {
+ continue;
+
+ } else if (dma_fence_is_later(tmp, next)) {
+ fences[i] = dma_fence_unwrap_next(&iter[i]);
+ goto restart;
+ } else {
+ fences[sel] = dma_fence_unwrap_next(&iter[sel]);
+ goto restart;
+ }
+ }
+
+ if (tmp) {
+ array[count++] = dma_fence_get(tmp);
+ fences[sel] = dma_fence_unwrap_next(&iter[sel]);
+ }
+ } while (tmp);
+
+ if (count == 0) {
+ tmp = dma_fence_allocate_private_stub(ktime_get());
+ goto return_tmp;
+ }
+
+ if (count == 1) {
+ tmp = array[0];
+ goto return_tmp;
+ }
+
+ result = dma_fence_array_create(count, array,
+ dma_fence_context_alloc(1),
+ 1, false);
+ if (!result) {
+ tmp = NULL;
+ goto return_tmp;
+ }
+ return &result->base;
+
+return_tmp:
+ kfree(array);
+ return tmp;
+}
+EXPORT_SYMBOL_GPL(__dma_fence_unwrap_merge);
diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c
index 394e6e1e9686..875ae4b3b047 100644
--- a/drivers/dma-buf/sync_file.c
+++ b/drivers/dma-buf/sync_file.c
@@ -384,13 +384,10 @@ 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 67382621b429..e827e8a83c4e 100644
--- a/drivers/gpu/drm/scheduler/sched_main.c
+++ b/drivers/gpu/drm/scheduler/sched_main.c
@@ -698,8 +698,7 @@ drm_sched_get_cleanup_job(struct drm_gpu_scheduler *sched)
typeof(*next), list);
if (next)
next->s_fence->scheduled.timestamp =
- job->s_fence->finished.timestamp;
-
+ dma_fence_timestamp(&job->s_fence->finished);
} else {
job = NULL;
/* queue timeout for next job */
diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h
index 6ffb4b2c6371..9d276655cc25 100644
--- a/include/linux/dma-fence.h
+++ b/include/linux/dma-fence.h
@@ -551,6 +551,25 @@ 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,
--
2.43.0
