linux-kernel - [PATCH] virtio_console: break out of buf poll on remove

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Date:   Tue, 5 Oct 2021 03:04:07 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     Amit Shah <amit@...nel.org>, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        virtualization@...ts.linux-foundation.org
Subject: [PATCH] virtio_console: break out of buf poll 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.

Fixing this comprehensively needs some thought, and new APIs.
Let's at least handle the specific case of virtio_console
removal that was reported in the field.

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1786239
Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
---
 drivers/char/virtio_console.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
index 7eaf303a7a86..c852ce0b4d56 100644
--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -1956,6 +1956,12 @@ static void virtcons_remove(struct virtio_device *vdev)
 	list_del(&portdev->list);
 	spin_unlock_irq(&pdrvdata_lock);
 
+	/* Device is going away, exit any polling for buffers */
+	virtio_break_device(vdev);
+	if (use_multiport(portdev))
+		flush_work(&portdev->control_work);
+	else
+		flush_work(&portdev->config_work);
 	/* Disable interrupts for vqs */
 	vdev->config->reset(vdev);
 	/* Finish up work that's lined up */
-- 
MST