FAILED: patch "[PATCH] xen-blkfront: unbind irq before tearing down ring and shadow" failed to apply to 5.15-stable tree

The patch below does not apply to the 5.15-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-5.15.y
git checkout FETCH_HEAD
git cherry-pick -x f3e27b7955727a4d7c0e9264a2a209fbba788bdc
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026110402-division-regulate-7540@gregkh' --subject-prefix 'PATCH 5.15.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

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

From f3e27b7955727a4d7c0e9264a2a209fbba788bdc Mon Sep 17 00:00:00 2001
From: Yuchao Zhang <[email protected]>
Date: Tue, 22 Sep 2026 15:21:55 +0800
Subject: [PATCH] xen-blkfront: unbind irq before tearing down ring and shadow
requests
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

In blkif_free_ring(), the driver tears down the ring's persistent grants, shadow request arrays, and shared ring structure (xenbus_teardown_ring), and only calls unbind_from_irqhandler() at the very end.

While blkif_free_ring() is freeing persistent grants and clearing the shadow array, the event channel interrupt (blkif_interrupt) is still registered and active. If an interrupt arrives from the backend during this teardown window, blkif_interrupt() reads rinfo->ring.sring and, via blkif_completion(), accesses rinfo->shadow[id].grants_used and rinfo->shadow[id].sg. blkif_free_ring() tears these structures down without holding rinfo->ring_lock, and the handler only checks info->connected at entry, so this is a real race resulting in a use-after-free or NULL pointer dereference.

Fix this by moving unbind_from_irqhandler() to the beginning of blkif_free_ring(). Calling unbind_from_irqhandler() first frees the IRQ and synchronizes with any in-flight interrupt handlers on other CPUs before ring memory and shadow request structures are deallocated, matching the teardown order in drivers/net/xen-netfront.c.

Message-ID: <[email protected]>

index 8dad7bf5f664..86f5dd3aced1 100644
@@ -1210,6 +1210,14 @@ static void blkif_free_ring(struct blkfront_ring_info *rinfo)
 	struct blkfront_info *info = rinfo->dev_info;
 	int i, j, segs;
 
+	/*
+	 * Interrupt teardown must be done ahead of freeing queue-related
+	 * data, otherwise the interrupt handler can race with the cleanup.
+	 */
+	if (rinfo->irq)
+		unbind_from_irqhandler(rinfo->irq, rinfo);
+	rinfo->evtchn = rinfo->irq = 0;
+
 	/*
 	 * Remove indirect pages, this only happens when using indirect
 	 * descriptors but not persistent grants

@@ -1292,10 +1300,6 @@ static void blkif_free_ring(struct blkfront_ring_info *rinfo)
 	/* Free resources associated with old device channel. */
 	xenbus_teardown_ring((void **)&rinfo->ring.sring, info->nr_ring_pages,
 			     rinfo->ring_ref);
-
-	if (rinfo->irq)
-		unbind_from_irqhandler(rinfo->irq, rinfo);
-	rinfo->evtchn = rinfo->irq = 0;
 }
 
 static void blkif_free(struct blkfront_info *info, int suspend)

From: Yuchao Zhang <[email protected]>

[ Upstream commit f3e27b7955727a4d7c0e9264a2a209fbba788bdc ]

In blkif_free_ring(), the driver tears down the ring's persistent grants, shadow request arrays, and shared ring structure (xenbus_teardown_ring), and only calls unbind_from_irqhandler() at the very end.

While blkif_free_ring() is freeing persistent grants and clearing the shadow array, the event channel interrupt (blkif_interrupt) is still registered and active. If an interrupt arrives from the backend during this teardown window, blkif_interrupt() reads rinfo->ring.sring and, via blkif_completion(), accesses rinfo->shadow[id].grants_used and rinfo->shadow[id].sg. blkif_free_ring() tears these structures down without holding rinfo->ring_lock, and the handler only checks info->connected at entry, so this is a real race resulting in a use-after-free or NULL pointer dereference.

Fix this by moving unbind_from_irqhandler() to the beginning of blkif_free_ring(). Calling unbind_from_irqhandler() first frees the IRQ and synchronizes with any in-flight interrupt handlers on other CPUs before ring memory and shadow request structures are deallocated, matching the teardown order in drivers/net/xen-netfront.c.

Message-ID: <[email protected]>

---
 drivers/block/xen-blkfront.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

index 831747ba8113c..02dc4a67ac82f 100644
@@ -1215,6 +1215,14 @@ static void blkif_free_ring(struct blkfront_ring_info *rinfo)
 	struct blkfront_info *info = rinfo->dev_info;
 	int i, j, segs;
 
+	/*
+	 * Interrupt teardown must be done ahead of freeing queue-related
+	 * data, otherwise the interrupt handler can race with the cleanup.
+	 */
+	if (rinfo->irq)
+		unbind_from_irqhandler(rinfo->irq, rinfo);
+	rinfo->evtchn = rinfo->irq = 0;
+
 	/*
 	 * Remove indirect pages, this only happens when using indirect
 	 * descriptors but not persistent grants

@@ -1304,10 +1312,6 @@ static void blkif_free_ring(struct blkfront_ring_info *rinfo)
 	free_pages_exact(rinfo->ring.sring,
 			 info->nr_ring_pages * XEN_PAGE_SIZE);
 	rinfo->ring.sring = NULL;
-
-	if (rinfo->irq)
-		unbind_from_irqhandler(rinfo->irq, rinfo);
-	rinfo->evtchn = rinfo->irq = 0;
 }
 
 static void blkif_free(struct blkfront_info *info, int suspend)

2.53.0