On 6/25/26 3:22 PM, Pavel Tikhomirov wrote: > > > On 6/4/26 17:46, Andrey Drobyshev wrote: >> During QEMU CPR live-update (and VHOST_RESET_OWNER in general) the guest >> keeps running while the host drops and later re-attaches vhost backends. >> If the guest adds a buffer to the TX virtqueue (guest->host) and kicks >> while the backend is temporarily NULL (between vhost_vsock_drop_backends() >> and the next vhost_vsock_start()), then the kick is delivered to the >> vhost worker, handle_tx_kick() sees a NULL backend and returns, and the >> kick signal is consumed. The buffer is then left in the ring. >> >> Then upon device start vhost_vsock_start() only re-kicks the RX send >> worker, never the TX VQ, so the buffer is processed only if the guest >> happens to kick again. But if the guest itself is now waiting for data >> from the host, it will never kick TX VQ again, and we end up in a >> deadlock. >> >> The deadlock is reproduced during active host->guest socat data transfer >> under multiple consecutive qemu-update's. >> >> To fix this, in vhost_vsock_start(), after kicking the RX send worker, also >> queue the TX vq poll so any buffers the guest enqueued while we were paused >> get scanned. >> >> https://virtuozzo.atlassian.net/browse/VSTOR-131956 >> https://virtuozzo.atlassian.net/browse/VSTOR-101116 > > Fixes: e541d8e1cf515 ("vhost/vsock: add VHOST_RESET_OWNER ioctl") > > right? >
Well kinda, but I deliberately added it as a standalone patch as it fixes a pre-existing issue, just this issue is only manifesting on RESET_OWNER. I also sent it upstream like that. >> >> Signed-off-by: Andrey Drobyshev <[email protected]> >> >> Feature: vhost-vsock: VHOST_RESET_OWNER ioctl >> --- >> drivers/vhost/vsock.c | 6 ++++++ >> 1 file changed, 6 insertions(+) >> >> diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c >> index 35f65b58108d..9aee012ababe 100644 >> --- a/drivers/vhost/vsock.c >> +++ b/drivers/vhost/vsock.c >> @@ -623,6 +623,12 @@ static int vhost_vsock_start(struct vhost_vsock *vsock) >> */ >> vhost_vq_work_queue(&vsock->vqs[VSOCK_VQ_RX], &vsock->send_pkt_work); >> >> + /* >> + * Some packets might've also been queued in TX VQ. Re-scan it here, >> + * mirroring the RX send-worker kick above. >> + */ >> + vhost_poll_queue(&vsock->vqs[VSOCK_VQ_TX].poll); >> + >> mutex_unlock(&vsock->dev.mutex); >> return 0; >> > _______________________________________________ Devel mailing list [email protected] https://lists.openvz.org/mailman/listinfo/devel
