Re: [PATCH 1/2] virtio-mmio: synchronize callbacks during device reset

virtio_reset_device() promises that vq callbacks are not in progress
once it returns, but vm_reset() only writes 0 to the status register.
A callback that has already entered vring_interrupt() keeps running
while the driver tears down the state it uses.

Wait for a status read to return 0, so the device has stopped raising
interrupts, then synchronize_irq() as vp_reset() does with
vp_synchronize_vectors().

Fixes: edfd52e63672 ("virtio: Add platform bus driver for memory mapped virtio device")
Assisted-by: Claude:claude-fable-5
Signed-off-by: Karl Mehltretter <redacted>
---
 drivers/virtio/virtio_mmio.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/virtio/virtio_mmio.c b/drivers/virtio/virtio_mmio.c
index 510b7c4efdff8..a2ca03dbe803d 100644
--- a/drivers/virtio/virtio_mmio.c
+++ b/drivers/virtio/virtio_mmio.c

@@ -55,6 +55,7 @@
 #define pr_fmt(fmt) "virtio-mmio: " fmt
 
 #include <linux/acpi.h>
+#include <linux/delay.h>
 #include <linux/dma-mapping.h>
 #include <linux/highmem.h>
 #include <linux/interrupt.h>

@@ -254,6 +255,11 @@ static void vm_reset(struct virtio_device *vdev)
 
 	/* 0 status means a reset. */
 	writel(0, vm_dev->base + VIRTIO_MMIO_STATUS);
+
+	/* Wait for reset completion before flushing callbacks. */
+	while (vm_get_status(vdev))
+		fsleep(1000);