Re: [Qemu-devel] [PATCH for 2.9 v3 10/10] block: Fix bdrv_co_flush early return

[Kevin Wolf <kwolf@redhat.com>]

Am 10.04.2017 um 17:05 hat Fam Zheng geschrieben:
> 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>
> ---
>  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);

As Coverity points out, we're now using bs...

> -    int current_gen = bs->write_gen;
> +    if (!bs || !bdrv_is_inserted(bs) || bdrv_is_read_only(bs) ||

...before doing the NULL check.

I'm not sure if we even need to have a NULL check here, but we would have
to check all callers to make sure that it's unnecessary. Before commit
29cdb251, it only checked bs->drv and I don't see how that commit
introduced a NULL caller, but maybe one was added later.

In any case, bdrv_co_flush() needs a fix, either remove the NULL check
or do it first.

> +        bdrv_is_sg(bs)) {
> +        goto early_exit;
> +    }

Kevin