Re: [PATCH 2/6] libvhost-user: Use slave_mutex in all slave messages

[Greg Kurz]

On Mon, 25 Jan 2021 13:01:11 -0500
Vivek Goyal <vgoyal@redhat.com> wrote:

> dev->slave_mutex needs to be taken when sending messages on slave_fd.
> Currently _vu_queue_notify() does not do that.
> 
> Introduce a helper vu_message_slave_send_receive() which sends as well
> as receive response. Use this helper in all the paths which send
> message on slave_fd channel.
> 

Does this fix any known bug ?

> Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
> ---

LGTM

Reviewed-by: Greg Kurz <groug@kaod.org>

>  subprojects/libvhost-user/libvhost-user.c | 50 ++++++++++++-----------
>  1 file changed, 27 insertions(+), 23 deletions(-)
> 
> diff --git a/subprojects/libvhost-user/libvhost-user.c 
> b/subprojects/libvhost-user/libvhost-user.c
> index 4cf4aef63d..7a56c56dc8 100644
> --- a/subprojects/libvhost-user/libvhost-user.c
> +++ b/subprojects/libvhost-user/libvhost-user.c
> @@ -403,7 +403,7 @@ vu_send_reply(VuDev *dev, int conn_fd, VhostUserMsg *vmsg)
>   * Processes a reply on the slave channel.
>   * Entered with slave_mutex held and releases it before exit.
>   * Returns true on success.
> - * *payload is written on success
> + * *payload is written on success, if payload is not NULL.
>   */
>  static bool
>  vu_process_message_reply(VuDev *dev, const VhostUserMsg *vmsg,
> @@ -427,7 +427,9 @@ vu_process_message_reply(VuDev *dev, const VhostUserMsg 
> *vmsg,
>          goto out;
>      }
>  
> -    *payload = msg_reply.payload.u64;
> +    if (payload) {
> +        *payload = msg_reply.payload.u64;
> +    }
>      result = true;
>  
>  out:
> @@ -435,6 +437,25 @@ out:
>      return result;
>  }
>  
> +/* Returns true on success, false otherwise */
> +static bool
> +vu_message_slave_send_receive(VuDev *dev, VhostUserMsg *vmsg, uint64_t 
> *payload)
> +{
> +    pthread_mutex_lock(&dev->slave_mutex);
> +    if (!vu_message_write(dev, dev->slave_fd, vmsg)) {
> +        pthread_mutex_unlock(&dev->slave_mutex);
> +        return false;
> +    }
> +
> +    if ((vmsg->flags & VHOST_USER_NEED_REPLY_MASK) == 0) {
> +        pthread_mutex_unlock(&dev->slave_mutex);
> +        return true;
> +    }
> +
> +    /* Also unlocks the slave_mutex */
> +    return vu_process_message_reply(dev, vmsg, payload);
> +}
> +
>  /* Kick the log_call_fd if required. */
>  static void
>  vu_log_kick(VuDev *dev)
> @@ -1340,16 +1361,8 @@ bool vu_set_queue_host_notifier(VuDev *dev, VuVirtq 
> *vq, int fd,
>          return false;
>      }
>  
> -    pthread_mutex_lock(&dev->slave_mutex);
> -    if (!vu_message_write(dev, dev->slave_fd, &vmsg)) {
> -        pthread_mutex_unlock(&dev->slave_mutex);
> -        return false;
> -    }
> -
> -    /* Also unlocks the slave_mutex */
> -    res = vu_process_message_reply(dev, &vmsg, &payload);
> +    res = vu_message_slave_send_receive(dev, &vmsg, &payload);
>      res = res && (payload == 0);
> -
>      return res;
>  }
>  
> @@ -2395,10 +2408,7 @@ static void _vu_queue_notify(VuDev *dev, VuVirtq *vq, 
> bool sync)
>              vmsg.flags |= VHOST_USER_NEED_REPLY_MASK;
>          }
>  
> -        vu_message_write(dev, dev->slave_fd, &vmsg);
> -        if (ack) {
> -            vu_message_read_default(dev, dev->slave_fd, &vmsg);
> -        }
> +        vu_message_slave_send_receive(dev, &vmsg, NULL);
>          return;
>      }
>  
> @@ -2942,17 +2952,11 @@ int64_t vu_fs_cache_request(VuDev *dev, 
> VhostUserSlaveRequest req, int fd,
>          return -EINVAL;
>      }
>  
> -    pthread_mutex_lock(&dev->slave_mutex);
> -    if (!vu_message_write(dev, dev->slave_fd, &vmsg)) {
> -        pthread_mutex_unlock(&dev->slave_mutex);
> -        return -EIO;
> -    }
> -
> -    /* Also unlocks the slave_mutex */
> -    res = vu_process_message_reply(dev, &vmsg, &payload);
> +    res = vu_message_slave_send_receive(dev, &vmsg, &payload);
>      if (!res) {
>          return -EIO;
>      }
> +
>      /*
>       * Payload is delivered as uint64_t but is actually signed for
>       * errors.