Re: [Qemu-devel] [PATCH] nbd: wait all read/write requests finished when shutdowning nbd socket

[Paolo Bonzini <pbonzini@redhat.com>]

On 16/09/2015 09:16, Wen Congyang wrote:
> If the socket fd is shutdown, there may be some data which is received before
> shutdown. We will read the data and do read/write in nbd_trip(). But the exp's
> blk is NULL, and it will cause qemu crashed.
> 
> Reported-by: Li Zhijian <lizhijian@cn.fujitsu.com>
> Signed-off-by: Wen Congyang <wency@cn.fujitsu.com>
> ---
>  nbd.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/nbd.c b/nbd.c
> index 06b501b..d8586a1 100644
> --- a/nbd.c
> +++ b/nbd.c
> @@ -1132,6 +1132,7 @@ void nbd_export_close(NBDExport *exp)
>      nbd_export_set_name(exp, NULL);
>      nbd_export_put(exp);
>      if (exp->blk) {
> +        bdrv_drain(blk_bs(exp->blk));
>          blk_remove_aio_context_notifier(exp->blk, blk_aio_attached,
>                                          blk_aio_detach, exp);
>          blk_unref(exp->blk);

I think a better fix is to move the whole "if" to nbd_export_put.  In
fact, nbd_export_close is wrong because exp can be freed by
nbd_export_close's call to nbd_export_put.

> @@ -1305,6 +1306,14 @@ static void nbd_trip(void *opaque)
>          goto invalid_request;
>      }
>  
> +    if (client->closing) {
> +        /*
> +         * The client may be closed when we are blocked in
> +         * nbd_co_receive_request()
> +         */
> +        goto done;
> +    }

This is okay.

Paolo

>      switch (command) {
>      case NBD_CMD_READ:
>          TRACE("Request type is READ");
>