[PATCH] dma-buf: fix check in dma_resv_add_fence

[Christian König]

It's valid to add the same fence multiple times to a dma-resv object and
we shouldn't need one extra slot for each.

Signed-off-by: Christian König <christian.koenig at amd.com>
Fixes: a3f7c10a269d5 ("dma-buf/dma-resv: check if the new fence is really later")
Cc: stable at vger.kernel.org # v5.19+
---
 drivers/dma-buf/dma-resv.c |  2 +-
 include/linux/dma-fence.h  | 15 +++++++++++++++
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/drivers/dma-buf/dma-resv.c b/drivers/dma-buf/dma-resv.c
index 38b4110378de..eb8b733065b2 100644
--- a/drivers/dma-buf/dma-resv.c
+++ b/drivers/dma-buf/dma-resv.c
@@ -301,7 +301,7 @@ void dma_resv_add_fence(struct dma_resv *obj, struct dma_fence *fence,
 
 		dma_resv_list_entry(fobj, i, obj, &old, &old_usage);
 		if ((old->context == fence->context && old_usage >= usage &&
-		     dma_fence_is_later(fence, old)) ||
+		     dma_fence_is_later_or_same(fence, old)) ||
 		    dma_fence_is_signaled(old)) {
 			dma_resv_list_set(fobj, i, fence, usage);
 			dma_fence_put(old);
diff --git a/include/linux/dma-fence.h b/include/linux/dma-fence.h
index ebe78bd3d121..b3772edca2e6 100644
--- a/include/linux/dma-fence.h
+++ b/include/linux/dma-fence.h
@@ -498,6 +498,21 @@ static inline bool dma_fence_is_later(struct dma_fence *f1,
 	return __dma_fence_is_later(f1->seqno, f2->seqno, f1->ops);
 }
 
+/**
+ * dma_fence_is_later_or_same - return true if f1 is later or same as f2
+ * @f1: the first fence from the same context
+ * @f2: the second fence from the same context
+ *
+ * Returns true if f1 is chronologically later than f2 or the same fence. Both
+ * fences must be from the same context, since a seqno is not re-used across
+ * contexts.
+ */
+static inline bool dma_fence_is_later_or_same(struct dma_fence *f1,
+					      struct dma_fence *f2)
+{
+	return f1 == f2 || dma_fence_is_later(f1, f2);
+}
+
 /**
  * dma_fence_later - return the chronologically later fence
  * @f1:	the first fence from the same context
-- 
2.34.1