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

[<gregkh@linuxfoundation.org>]

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 <stable@vger.kernel.org>.

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 '<stable@vger.kernel.org>' --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 <hjeong.choi@samsung.com>
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.

Signed-off-by: Hyejeong Choi <hjeong.choi@samsung.com>
Fixes: a590d0fdbaa5 ("dma-buf: Update reservation shared_count after adding the new fence")
CC: stable@vger.kernel.org
Reviewed-by: Christian König <christian.koenig@amd.com>
Link: https://lore.kernel.org/r/20250513020638.GA2329653@au1-maretx-p37.eng.sarc.samsung.com
Signed-off-by: Christian König <christian.koenig@amd.com>

diff --git a/drivers/dma-buf/dma-resv.c b/drivers/dma-buf/dma-resv.c
index 5f8d010516f0..b1ef4546346d 100644
--- a/drivers/dma-buf/dma-resv.c
+++ b/drivers/dma-buf/dma-resv.c
@@ -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);