Re: [PATCH 1/5] vhost-user-blk: Don't reconnect during initialisation

[Philippe Mathieu-Daudé]

On 4/22/21 7:02 PM, Kevin Wolf wrote:
> This is a partial revert of commits 77542d43149 and bc79c87bcde.
> 
> Usually, an error during initialisation means that the configuration was
> wrong. Reconnecting won't make the error go away, but just turn the
> error condition into an endless loop. Avoid this and return errors
> again.
> 
> Additionally, calling vhost_user_blk_disconnect() from the chardev event
> handler could result in use-after-free because none of the
> initialisation code expects that the device could just go away in the

TIL initialisation wording.

> middle. So removing the call fixes crashes in several places.
> 
> For example, using a num-queues setting that is incompatible with the
> backend would result in a crash like this (dereferencing dev->opaque,
> which is already NULL):
> 
>  #0  0x0000555555d0a4bd in vhost_user_read_cb (source=0x5555568f4690, 
> condition=(G_IO_IN | G_IO_HUP), opaque=0x7fffffffcbf0) at 
> ../hw/virtio/vhost-user.c:313
>  #1  0x0000555555d950d3 in qio_channel_fd_source_dispatch 
> (source=0x555557c3f750, callback=0x555555d0a478 <vhost_user_read_cb>, 
> user_data=0x7fffffffcbf0) at ../io/channel-watch.c:84
>  #2  0x00007ffff7b32a9f in g_main_context_dispatch () at 
> /lib64/libglib-2.0.so.0
>  #3  0x00007ffff7b84a98 in g_main_context_iterate.constprop () at 
> /lib64/libglib-2.0.so.0
>  #4  0x00007ffff7b32163 in g_main_loop_run () at /lib64/libglib-2.0.so.0
>  #5  0x0000555555d0a724 in vhost_user_read (dev=0x555557bc62f8, 
> msg=0x7fffffffcc50) at ../hw/virtio/vhost-user.c:402
>  #6  0x0000555555d0ee6b in vhost_user_get_config (dev=0x555557bc62f8, 
> config=0x555557bc62ac "", config_len=60) at ../hw/virtio/vhost-user.c:2133
>  #7  0x0000555555d56d46 in vhost_dev_get_config (hdev=0x555557bc62f8, 
> config=0x555557bc62ac "", config_len=60) at ../hw/virtio/vhost.c:1566
>  #8  0x0000555555cdd150 in vhost_user_blk_device_realize (dev=0x555557bc60b0, 
> errp=0x7fffffffcf90) at ../hw/block/vhost-user-blk.c:510
>  #9  0x0000555555d08f6d in virtio_device_realize (dev=0x555557bc60b0, 
> errp=0x7fffffffcff0) at ../hw/virtio/virtio.c:3660
> 
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>  hw/block/vhost-user-blk.c | 54 ++++++++++-----------------------------
>  1 file changed, 13 insertions(+), 41 deletions(-)