Re: [PATCH v2 2/3] virtio_input: stop callbacks before unregistering input device
From: "Michael S. Tsirkin" <mst@redhat.com>
Date: 2026-09-06 06:52:07
Also in:
kvm, linux-remoteproc, linux-s390, linux-um, lkml, platform-driver-x86, virtualization
On Sat, Sep 05, 2026 at 05:20:58PM +0200, Karl Mehltretter wrote:
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.
And now I am completely confused. So it is other transports you are worried about? Which ones did you test? And why don't you worry about fixing other transports in 1/3?
Fixes: 271c865161c5 ("Add virtio-input driver.")
Assisted-by: LLM
Signed-off-by: Karl Mehltretter <redacted>quoted hunk ↗ jump to hunk
--- 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)