Re: [Qemu-devel] [PATCH 11/18] vhost-user: add shutdown support

[Yuanhan Liu <yuanhan.liu@linux.intel.com>]

On Wed, Apr 13, 2016 at 05:51:15AM -0400, Marc-André Lureau wrote:
> Hi
> 
> ----- Original Message -----
> > Hi Marc,
> > 
> > First of all, sorry again for late response!
> > 
> > Last time I tried with your first version, I found few issues related
> > with reconnect, mainly on the acked_feautres lost. While checking your
> > new code, I found that you've already solved that, which is great.
> > 
> > So, I tried harder this time, your patches work great, except that I
> > found few nits.
> > 
> > On Fri, Apr 01, 2016 at 01:16:21PM +0200, marcandre.lureau@redhat.com wrote:
> > > From: Marc-André Lureau <marcandre.lureau@redhat.com>
> > ...
> > > +Slave message types
> > > +-------------------
> > > +
> > > + * VHOST_USER_SLAVE_SHUTDOWN:
> > > +      Id: 1
> > > +      Master payload: N/A
> > > +      Slave payload: u64
> > > +
> > > +      Request the master to shutdown the slave. A 0 reply is for
> > > +      success, in which case the slave may close all connections
> > > +      immediately and quit.
> > 
> > Assume we are using ovs + dpdk here, that we could have two
> > vhost-user connections. While ovs tries to initiate a restart,
> > it might unregister the two connections one by one. In such
> > case, two VHOST_USER_SLAVE_SHUTDOWN request will be sent,
> > and two replies will get. Therefore, I don't think it's a
> > proper ask here to let the backend implementation to do quit
> > here.
> > 
> 
> On success reply, the master sent all the commands to finish the connection. So the slave must flush/finish all pending requests first.

Yes, that's okay. I here just mean the "close __all__ connections"
and "quit" part.

Firstly, we should do cleanup/flush/finish to it's own connection.
But not all, right?

Second, as stated, doing quit might not make sense, as we may
have more connections.

> I think this should be enough, otherwise we may need a new explicit message?
> 
> > 
> > >  
> > >      switch (msg.request) {
> > > +    case VHOST_USER_SLAVE_SHUTDOWN: {
> > > +        uint64_t success = 1; /* 0 is for success */
> > > +        if (dev->stop) {
> > > +            dev->stop(dev);
> > > +            success = 0;
> > > +        }
> > > +        msg.payload.u64 = success;
> > > +        msg.size = sizeof(msg.payload.u64);
> > > +        size = send(u->slave_fd, &msg, VHOST_USER_HDR_SIZE + msg.size, 0);
> > > +        if (size != VHOST_USER_HDR_SIZE + msg.size) {
> > > +            error_report("Failed to write reply.");
> > > +        }
> > > +        break;
> > 
> > You might want to remove the slave_fd from watch list? We
> > might also need to close slave_fd here, assuming that we
> > will no longer use it when VHOST_USER_SLAVE_SHUTDOWN is
> > received?
> 
> Makes sense, I will change that in next update.
> 
> > I'm asking because I found a seg fault issue sometimes,
> > due to opaque is NULL.

Oh, I was wrong, it's u being NULL, but not opaque.
> >
> 
> I would be interested to see the backtrace or have a reproducer.

It's a normal test steps: start a vhost-user switch (I'm using DPDK
vhost-switch example), kill it, and wait for a while (something like
more than 10s or even longer), then I saw a seg fault:

    (gdb) p dev
    $4 = (struct vhost_dev *) 0x555556571bf0
    (gdb) p u
    $5 = (struct vhost_user *) 0x0
    (gdb) where
    #0  0x0000555555798612 in slave_read (opaque=0x555556571bf0)
        at /home/yliu/qemu/hw/virtio/vhost-user.c:539
    #1  0x0000555555a343a4 in aio_dispatch (ctx=0x55555655f560) at /home/yliu/qemu/aio-posix.c:327
    #2  0x0000555555a2738b in aio_ctx_dispatch (source=0x55555655f560, callback=0x0, user_data=0x0)
        at /home/yliu/qemu/async.c:233
    #3  0x00007ffff51032a6 in g_main_context_dispatch () from /lib64/libglib-2.0.so.0
    #4  0x0000555555a3239e in glib_pollfds_poll () at /home/yliu/qemu/main-loop.c:213
    #5  0x0000555555a3247b in os_host_main_loop_wait (timeout=29875848) at /home/yliu/qemu/main-loop.c:258
    #6  0x0000555555a3252b in main_loop_wait (nonblocking=0) at /home/yliu/qemu/main-loop.c:506
    #7  0x0000555555846e35 in main_loop () at /home/yliu/qemu/vl.c:1934
    #8  0x000055555584e6bf in main (argc=31, argv=0x7fffffffe078, envp=0x7fffffffe178)
        at /home/yliu/qemu/vl.c:4658


	--yliu