Re: [Qemu-devel] [PULL 10/11] block: Fix bdrv_co_flush early return

[Peter Maydell <peter.maydell@linaro.org>]

On 11 April 2017 at 13:26, Fam Zheng <famz@redhat.com> wrote:
> bdrv_inc_in_flight and bdrv_dec_in_flight are mandatory for
> BDRV_POLL_WHILE to work, even for the shortcut case where flush is
> unnecessary. Move the if block to below bdrv_dec_in_flight, and BTW fix
> the variable declaration position.
>
> Signed-off-by: Fam Zheng <famz@redhat.com>
> Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
> Reviewed-by: Kevin Wolf <kwolf@redhat.com>
> Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  block/io.c | 16 +++++++++-------
>  1 file changed, 9 insertions(+), 7 deletions(-)
>
> diff --git a/block/io.c b/block/io.c
> index 00e45ca..bae6947 100644
> --- a/block/io.c
> +++ b/block/io.c
> @@ -2278,16 +2278,17 @@ static void coroutine_fn bdrv_flush_co_entry(void *opaque)
>
>  int coroutine_fn bdrv_co_flush(BlockDriverState *bs)
>  {
> -    int ret;
> -
> -    if (!bs || !bdrv_is_inserted(bs) || bdrv_is_read_only(bs) ||
> -        bdrv_is_sg(bs)) {
> -        return 0;
> -    }
> +    int current_gen;
> +    int ret = 0;
>
>      bdrv_inc_in_flight(bs);
>
> -    int current_gen = bs->write_gen;
> +    if (!bs || !bdrv_is_inserted(bs) || bdrv_is_read_only(bs) ||
> +        bdrv_is_sg(bs)) {
> +        goto early_exit;
> +    }

Coverity points out that there's a problem here -- we call
bdrv_inc_in_flight(bs), which assumes bs is not NULL, before
we do the test for whether bs is NULL.

Presumably the NULL check needs to be pulled up earlier in
the function?

thanks
-- PMM