linux-kernel - [PATCH AUTOSEL 4.9 1/2] virtio_console: break out of buf poll on remove

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Date:   Wed, 16 Mar 2022 10:19:07 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     "Michael S. Tsirkin" <mst@...hat.com>,
        Sasha Levin <sashal@...nel.org>, amit@...nel.org,
        gregkh@...uxfoundation.org,
        virtualization@...ts.linux-foundation.org
Subject: [PATCH AUTOSEL 4.9 1/2] virtio_console: break out of buf poll on remove

From: "Michael S. Tsirkin" <mst@...hat.com>

[ Upstream commit 0e7174b9d5877130fec41fb4a16e0c2ee4958d44 ]

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>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 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 2632b0fdb1b5..a6b6dc204c1f 100644
--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -2004,6 +2004,13 @@ 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 */
 	vdev->config->reset(vdev);
 	/* Finish up work that's lined up */
-- 
2.34.1