Re: [PATCH v7 1/7] block: add a sanity check for non-write flush/fua bios

[Niklas Cassel <Niklas.Cassel@wdc.com>]

On Tue, Jan 03, 2023 at 02:19:18PM +0900, Damien Le Moal wrote:
> From: Christoph Hellwig <hch@infradead.org>
>
> Check that the PREFUSH and FUA flags are only set on write bios,
> given that the flush state machine expects that.
>
> [Damien] The check is also extended to REQ_OP_ZONE_APPEND operations as
> these are data write operations used by btrfs and zonefs and may also
> have the REQ_FUA bit set.
>
> Reported-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>
> ---
>  block/blk-core.c | 14 +++++++++-----
>  1 file changed, 9 insertions(+), 5 deletions(-)
>
> diff --git a/block/blk-core.c b/block/blk-core.c
> index 9321767470dc..c644aac498ef 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -744,12 +744,16 @@ void submit_bio_noacct(struct bio *bio)
>	 * Filter flush bio's early so that bio based drivers without flush
>	 * support don't have to worry about them.
>	 */
> -	if (op_is_flush(bio->bi_opf) &&
> -	    !test_bit(QUEUE_FLAG_WC, &q->queue_flags)) {
> -		bio->bi_opf &= ~(REQ_PREFLUSH | REQ_FUA);
> -		if (!bio_sectors(bio)) {
> -			status = BLK_STS_OK;
> +	if (op_is_flush(bio->bi_opf)) {
> +		if (WARN_ON_ONCE(bio_op(bio) != REQ_OP_WRITE &&
> +				 bio_op(bio) != REQ_OP_ZONE_APPEND))
>			goto end_io;
> +		if (!test_bit(QUEUE_FLAG_WC, &q->queue_flags)) {
> +			bio->bi_opf &= ~(REQ_PREFLUSH | REQ_FUA);
> +			if (!bio_sectors(bio)) {
> +				status = BLK_STS_OK;
> +				goto end_io;
> +			}
>		}
>	}

Hello Damien,

In a previous email I wrote:

> It seems that you can have flag WC set, without having flag FUA set.
>
> So should perhaps the line:
>
>> +             if (!test_bit(QUEUE_FLAG_WC, &q->queue_flags)) {
>
> instead be:
>
> if (!test_bit(QUEUE_FLAG_FUA, &q->queue_flags)) {

You replied with:
"Need both. If there is no write cache or write cache is off, FUA is
implied and is useless."

Did you change your mind since then?


Kind regards,
Niklas