[PATCH v2 2/3] virtio_input: stop callbacks before unregistering input device

[Karl Mehltretter <kmehltretter@gmail.com>]

virtinput_remove() unregisters the input device before resetting the
virtio device. virtinput_recv_events() drops vi->lock around input_event(),
so clearing vi->ready does not stop a callback that passed the entry check.
It can still use vi->idev, requeue buffers and kick the queue.

Reset first, as virtinput_freeze() already does. With the preceding core
change, reset waits for callbacks before input_unregister_device() can
free vi->idev. Recheck vi->ready after taking the lock again: keep draining
completed events so an input packet is not truncated, but stop requeueing
buffers and kicking the queue.

With evdev attached, input_unregister_handle() currently waits for an RCU
grace period, which also waits out IRQ callbacks. This masks the lifetime
bug on PCI and MMIO, but does not protect sleepable callbacks on other
transports.

Fixes: 271c865161c5 ("Add virtio-input driver.")
Assisted-by: LLM
Signed-off-by: Karl Mehltretter <kmehltretter@gmail.com>
---
 drivers/virtio/virtio_input.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/virtio/virtio_input.c b/drivers/virtio/virtio_input.c
index deec24e8e682..7b654af0a42c 100644
--- a/drivers/virtio/virtio_input.c
+++ b/drivers/virtio/virtio_input.c
@@ -49,9 +49,12 @@ static void virtinput_recv_events(struct virtqueue *vq)
 				    le16_to_cpu(event->code),
 				    le32_to_cpu(event->value));
 			spin_lock_irqsave(&vi->lock, flags);
+			if (!vi->ready)
+				continue;
 			virtinput_queue_evtbuf(vi, event);
 		}
-		virtqueue_kick(vq);
+		if (vi->ready)
+			virtqueue_kick(vq);
 	}
 	spin_unlock_irqrestore(&vi->lock, flags);
 }
@@ -350,8 +353,9 @@ static void virtinput_remove(struct virtio_device *vdev)
 	vi->ready = false;
 	spin_unlock_irqrestore(&vi->lock, flags);
 
-	input_unregister_device(vi->idev);
+	/* Callbacks use vi->idev. */
 	virtio_reset_device(vdev);
+	input_unregister_device(vi->idev);
 	while ((buf = virtqueue_detach_unused_buf(vi->sts)) != NULL)
 		kfree(buf);
 	vdev->config->del_vqs(vdev);
-- 
2.39.5 (Apple Git-154)