FAILED: patch "[PATCH] dma-buf: insert memory barrier before updating num_fences" failed to apply to 5.10-stable tree

The patch below does not apply to the 5.10-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-5.10.y
git checkout FETCH_HEAD
git cherry-pick -x 72c7d62583ebce7baeb61acce6057c361f73be4a
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2025051949-keep-opposing-04c8@gregkh' --subject-prefix 'PATCH 5.10.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

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

From 72c7d62583ebce7baeb61acce6057c361f73be4a Mon Sep 17 00:00:00 2001
From: Hyejeong Choi <[email protected]>
Date: Mon, 12 May 2025 21:06:38 -0500
Subject: [PATCH] dma-buf: insert memory barrier before updating num_fences
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

smp_store_mb() inserts memory barrier after storing operation. It is different with what the comment is originally aiming so Null pointer dereference can be happened if memory update is reordered.

index 5f8d010516f0..b1ef4546346d 100644
@@ -320,8 +320,9 @@ void dma_resv_add_fence(struct dma_resv *obj, struct dma_fence *fence,
 	count++;
 
 	dma_resv_list_set(fobj, i, fence, usage);
-	/* pointer update must be visible before we extend the num_fences */
-	smp_store_mb(fobj->num_fences, count);
+	/* fence update must be visible before we extend the num_fences */
+	smp_wmb();
+	fobj->num_fences = count;
 }
 EXPORT_SYMBOL(dma_resv_add_fence);