RE: [PATCH net] vsock/virtio: discard packets only when socket is really closed

[Justin He]

> -----Original Message-----
> From: Stefano Garzarella <sgarzare@xxxxxxxxxx>
> Sent: Friday, November 20, 2020 6:48 PM
> To: netdev@xxxxxxxxxxxxxxx
> Cc: Sergio Lopez <slp@xxxxxxxxxx>; David S. Miller <davem@xxxxxxxxxxxxx>;
> Stefano Garzarella <sgarzare@xxxxxxxxxx>; Justin He <Justin.He@xxxxxxx>;
> kvm@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; Stefan Hajnoczi
> <stefanha@xxxxxxxxxx>; virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx; Jakub
> Kicinski <kuba@xxxxxxxxxx>
> Subject: [PATCH net] vsock/virtio: discard packets only when socket is
> really closed
>
> Starting from commit 8692cefc433f ("virtio_vsock: Fix race condition
> in virtio_transport_recv_pkt"), we discard packets in
> virtio_transport_recv_pkt() if the socket has been released.
>
> When the socket is connected, we schedule a delayed work to wait the
> RST packet from the other peer, also if SHUTDOWN_MASK is set in
> sk->sk_shutdown.
> This is done to complete the virtio-vsock shutdown algorithm, releasing
> the port assigned to the socket definitively only when the other peer
> has consumed all the packets.
>
> If we discard the RST packet received, the socket will be closed only
> when the VSOCK_CLOSE_TIMEOUT is reached.
>
> Sergio discovered the issue while running ab(1) HTTP benchmark using
> libkrun [1] and observing a latency increase with that commit.
>
> To avoid this issue, we discard packet only if the socket is really
> closed (SOCK_DONE flag is set).
> We also set SOCK_DONE in virtio_transport_release() when we don't need
> to wait any packets from the other peer (we didn't schedule the delayed
> work). In this case we remove the socket from the vsock lists, releasing
> the port assigned.
>
> [1] https://github.com/containers/libkrun
>
> Fixes: 8692cefc433f ("virtio_vsock: Fix race condition in
> virtio_transport_recv_pkt")

Acked-by: Jia He <justin.he@xxxxxxx>


--
Cheers,
Justin (Jia He)


> Cc: justin.he@xxxxxxx
> Reported-by: Sergio Lopez <slp@xxxxxxxxxx>
> Tested-by: Sergio Lopez <slp@xxxxxxxxxx>
> Signed-off-by: Stefano Garzarella <sgarzare@xxxxxxxxxx>
> ---
>  net/vmw_vsock/virtio_transport_common.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/net/vmw_vsock/virtio_transport_common.c
> b/net/vmw_vsock/virtio_transport_common.c
> index 0edda1edf988..5956939eebb7 100644
> --- a/net/vmw_vsock/virtio_transport_common.c
> +++ b/net/vmw_vsock/virtio_transport_common.c
> @@ -841,8 +841,10 @@ void virtio_transport_release(struct vsock_sock *vsk)
>  virtio_transport_free_pkt(pkt);
>  }
>
> -if (remove_sock)
> +if (remove_sock) {
> +sock_set_flag(sk, SOCK_DONE);
>  vsock_remove_sock(vsk);
> +}
>  }
>  EXPORT_SYMBOL_GPL(virtio_transport_release);
>
> @@ -1132,8 +1134,8 @@ void virtio_transport_recv_pkt(struct
> virtio_transport *t,
>
>  lock_sock(sk);
>
> -/* Check if sk has been released before lock_sock */
> -if (sk->sk_shutdown == SHUTDOWN_MASK) {
> +/* Check if sk has been closed before lock_sock */
> +if (sock_flag(sk, SOCK_DONE)) {
>  (void)virtio_transport_reset_no_sock(t, pkt);
>  release_sock(sk);
>  sock_put(sk);
> --
> 2.26.2

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