Re: [PATCH 1/2] block/io: Update BSC only if want_zero is true

[Nir Soffer]

On Mon, Jan 17, 2022 at 6:26 PM Hanna Reitz <hreitz@redhat.com> wrote:
>
> We update the block-status cache whenever we get new information from a
> bdrv_co_block_status() call to the block driver.  However, if we have
> passed want_zero=false to that call, it may flag areas containing zeroes
> as data, and so we would update the block-status cache with wrong
> information.
>
> Therefore, we should not update the cache with want_zero=false.
>
> Reported-by: Nir Soffer <nsoffer@redhat.com>
> Fixes: 0bc329fbb009f8601cec23bf2bc48ead0c5a5fa2
>        ("block: block-status cache for data regions")
> Signed-off-by: Hanna Reitz <hreitz@redhat.com>
> ---
>  block/io.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/block/io.c b/block/io.c
> index bb0a254def..4e4cb556c5 100644
> --- a/block/io.c
> +++ b/block/io.c
> @@ -2497,8 +2497,12 @@ static int coroutine_fn 
> bdrv_co_block_status(BlockDriverState *bs,
>               * non-protocol nodes, and then it is never used.  However, 
> filling
>               * the cache requires an RCU update, so double check here to 
> avoid
>               * such an update if possible.
> +             *
> +             * Check want_zero, because we only want to update the cache 
> when we
> +             * have accurate information about what is zero and what is data.
>               */
> -            if (ret == (BDRV_BLOCK_DATA | BDRV_BLOCK_OFFSET_VALID) &&
> +            if (want_zero &&
> +                ret == (BDRV_BLOCK_DATA | BDRV_BLOCK_OFFSET_VALID) &&
>                  QLIST_EMPTY(&bs->children))
>              {
>                  /*
> --
> 2.33.1
>

ovirt-imageio tests pass with this change.
Thanks for the quick fix!

Reviewed-by: Nir Soffer <nsoffer@redhat.com>