linux-kernel - [PATCH v2 2/3] virtio_console: break out of buf poll on remove

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Message-ID: <20220114215641.239984-3-mst@redhat.com>
Date:   Fri, 14 Jan 2022 16:57:27 -0500
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 v2 2/3] 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.

Fix this up by calling virtio_break_device + flush before reset.

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1786239
Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
---
 drivers/char/virtio_console.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
index 2359889a35a0..e3c430539a17 100644
--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -1957,6 +1957,13 @@ 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 */
 	virtio_reset_device(vdev);
 	/* Finish up work that's lined up */
-- 
MST