linux-kernel - [PATCH] virtio_mem: break device on remove

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Date:   Fri, 14 Jan 2022 16:43:26 -0500
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     David Hildenbrand <david@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        virtualization@...ts.linux-foundation.org
Subject: [PATCH] virtio_mem: break device on remove

A common pattern for device reset is currently:
vdev->config->reset(vdev);
.. cleanup ..

reset prevents new interrupts from arriving and waits for interrupt
handlers to finish.

However if - as is common - the handler queues a work request which is
flushed during the cleanup stage, we have code adding buffers / trying
to get buffers while device is reset. Not good.

This was reproduced by running
	modprobe virtio_console
	modprobe -r virtio_console
in a loop, and this reasoning seems to apply to virtio mem though
I could not reproduce it there.

Fix this up by calling virtio_break_device + flush before reset.

Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
---
 drivers/virtio/virtio_mem.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/virtio/virtio_mem.c b/drivers/virtio/virtio_mem.c
index 38becd8d578c..33b8a118a3ae 100644
--- a/drivers/virtio/virtio_mem.c
+++ b/drivers/virtio/virtio_mem.c
@@ -2888,6 +2888,8 @@ static void virtio_mem_remove(struct virtio_device *vdev)
 		virtio_mem_deinit_hotplug(vm);
 
 	/* reset the device and cleanup the queues */
+	virtio_break_device(vdev);
+	flush_work(&vm->wq);
 	virtio_reset_device(vdev);
 	vdev->config->del_vqs(vdev);
 
-- 
MST