Re: [dpdk-stable] [dpdk-dev] [PATCH] vhost: fix deadlock when vhost unregister

[孙文杰 <findtheonlyway@gmail.com>]

Thanks, Maxime.

Your description is better, My real name is Wenjie Sun.

Signed-off-by: Wenjie Sun <findtheonlyway@gmail.com>

Maxime Coquelin <maxime.coquelin@redhat.com> 于2019年2月8日周五 下午10:12写道：

>
>
> On 1/28/19 7:55 AM, sunwenjie wrote:
> > When rte_vhost_driver_unregister  delete the connection fd,
> > fdset_try_del will always try and donot release the
> > vhostuser.mutex if the fd is busy, but the fdset_event_dispatch
> > will set the  fd to busy and call vhost_user_msg_handler to get
> > vhostuser.mutex, which will  cause deadlock. Unlock the
> > vhost_user.mutexif fdset_try_del fail and relock it when retry.
>
> What about this wording:
>
> In rte_vhost_driver_unregister(), the connection fd is removed from
> the fdset using fdset_try_del(). Call to this function may fail
> if the corresponding fd is in busy state, indicating that event
> dispatcher is executing the read or write callback on this fd.
> When it happens, rte_vhost_driver_unregister() keeps trying to
> remove the fd from the set until it is no more busy.
>
> This situation is causing a deadlock, because
> rte_vhost_driver_unregister() keeps trying to remove the fd from
> the set with vhost_user.mutex held, while the callback executed
> by the dispatcher, vhost_user_read_cb(), also takes this mutex at
> numerous places.
>
> The fix consists in releasing vhost_user.mutex between each retry
> in vhost_driver_unregister().
>
>
> >
> > Fixes: 8b4b949144b8 ("vhost: fix dead lock on closing in server mode")
> > Cc: stable@dpdk.org
> >
> > Signed-off-by: sunwenjie <findtheonlyway@gmail.com>
>
> We need your real name for legal reasons:
> Signed-off-by: Surname Lastname <findtheonlyway@gmail.com>
>
> No need to resubmit, I can handle the commit message fixup and
> the fix looks good to me:
> Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>
>
> As soon as I get your name in above format I will apply the patch in
> Virtio tree. Thanks for submitting the fix.
>
> Maxime
> > ---
> >   lib/librte_vhost/socket.c | 3 ++-
> >   1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/lib/librte_vhost/socket.c b/lib/librte_vhost/socket.c
> > index 9cf34ad17..9883b0491 100644
> > --- a/lib/librte_vhost/socket.c
> > +++ b/lib/librte_vhost/socket.c
> > @@ -961,13 +961,13 @@ rte_vhost_driver_unregister(const char *path)
> >       int count;
> >       struct vhost_user_connection *conn, *next;
> >
> > +again:
> >       pthread_mutex_lock(&vhost_user.mutex);
> >
> >       for (i = 0; i < vhost_user.vsocket_cnt; i++) {
> >               struct vhost_user_socket *vsocket = vhost_user.vsockets[i];
> >
> >               if (!strcmp(vsocket->path, path)) {
> > -again:
> >                       pthread_mutex_lock(&vsocket->conn_mutex);
> >                       for (conn = TAILQ_FIRST(&vsocket->conn_list);
> >                            conn != NULL;
> > @@ -983,6 +983,7 @@ rte_vhost_driver_unregister(const char *path)
> >                                                 conn->connfd) == -1) {
> >                                       pthread_mutex_unlock(
> >
>  &vsocket->conn_mutex);
> > +
>  pthread_mutex_unlock(&vhost_user.mutex);
> >                                       goto again;
> >                               }
> >
> >
>