From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: stable@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	patches@lists.linux.dev,
	"Michael S. Tsirkin" <mst@redhat.com>,
	Andrew Stellman <astellman@stellman-greene.com>,
	Sasha Levin <sashal@kernel.org>
Subject: [PATCH 6.18 0859/1250] virtio-pci: return IRQ_HANDLED after non-zero ISR
Date: Thu, 17 Sep 2026 16:10:54 +0100
Message-ID: <20260917151615.251127844@linuxfoundation.org>
In-Reply-To: <20260917151551.901433442@linuxfoundation.org>
References: <20260917151551.901433442@linuxfoundation.org>
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6.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Andrew Stellman <astellman@stellman-greene.com>

[ Upstream commit 93fa09455fb1a9624b73d42ac1f83771f4818e80 ]

vp_interrupt() reads the ISR before dispatching config-change and
vring handling. Reading the ISR also clears it, so once the read
returns non-zero the interrupt was from this device and has already
been consumed.

Currently vp_interrupt() returns the result of vp_vring_interrupt().
For a config-change interrupt with no vring work, that can return
IRQ_NONE even though the ISR was non-zero and the interrupt was
handled.

Call vp_vring_interrupt() for any queue work, but once the ISR is
non-zero return IRQ_HANDLED.

Tested with QEMU virtio-blk-pci forced to INTx using vectors=0 and
pci=nomsi. On an idle device, 200 config-change interrupts were
generated using QMP block_resize.

Before this change, irq_handler_exit reported ret=unhandled and
/proc/irq/11/spurious increased from 0 to 200 unhandled interrupts.
After this change, irq_handler_exit reported ret=handled and the
unhandled count remained at 0.

The issue was found during an LLM-assisted Quality Playbook review.

Fixes: 77cf524654a8 ("virtio_pci: split up vp_interrupt")
Suggested-by: Michael S. Tsirkin <mst@redhat.com>
Assisted-by: LLM
Signed-off-by: Andrew Stellman <astellman@stellman-greene.com>
Message-ID: <20260904141318.30278-1-astellman@stellman-greene.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/virtio/virtio_pci_common.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/virtio/virtio_pci_common.c b/drivers/virtio/virtio_pci_common.c
index ef87e7584756e..64806d042dbb2 100644
--- a/drivers/virtio/virtio_pci_common.c
+++ b/drivers/virtio/virtio_pci_common.c
@@ -120,7 +120,9 @@ static irqreturn_t vp_interrupt(int irq, void *opaque)
 	if (isr & VIRTIO_PCI_ISR_CONFIG)
 		vp_config_changed(irq, opaque);
 
-	return vp_vring_interrupt(irq, opaque);
+	vp_vring_interrupt(irq, opaque);
+
+	return IRQ_HANDLED;
 }
 
 static int vp_request_msix_vectors(struct virtio_device *vdev, int nvectors,
-- 
2.53.0