[Devel] [RFC PATCH vz9 v6 59/62] dm-ploop: fix how ENOTBLK is handled

[Andrey Zhadchenko]

On 12/5/24 22:56, Alexander Atanasov wrote:
> direct IO  write result ENOTBLK or 0(in ext4 case) means
> retry IO in buffered mode. We wrongly assumed that it is
> a short write and handled it incorrectly
> 
> Since we can not retry in buffered mode, code is not ready
> for it. Take a different route. This error happens if
> page invalidation fails, which is a very rare situation.
> So call synchronize_rcu() and just resubmit pio.
> 
> https://virtuozzo.atlassian.net/browse/VSTOR-91821
> Suggested-by: Alexey Kuznetsov <kuznet at virtuozzo.com>
> Signed-off-by: Alexander Atanasov <alexander.atanasov at virtuozzo.com>
> ---
>   drivers/md/dm-ploop-map.c | 25 ++++++++++++++++---------
>   1 file changed, 16 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/md/dm-ploop-map.c b/drivers/md/dm-ploop-map.c
> index a03e1af3fd87..482022d6b60b 100644
> --- a/drivers/md/dm-ploop-map.c
> +++ b/drivers/md/dm-ploop-map.c
> @@ -1312,24 +1312,31 @@ static void ploop_data_rw_complete(struct pio *pio)
>   	bool completed;
>   
>   	if (pio->ret != pio->bi_iter.bi_size) {
> -		if (pio->ret >= 0) {
> -			/* Partial IO */
> -			WARN_ON_ONCE(pio->ret == 0);
> -			/* Do not resubmit zero length pio */
> +		if (pio->ret >= 0 || pio->ret == -ENOTBLK) {
> +			/* Partial IO or request to retry in buffered mode */
> +			if (pio->ret == 0 || pio->ret == -ENOTBLK) {
> +				/*
> +				 * ENOTBLK means we should retry in buffered io
> +				 * but we can not, so try again in DIO
> +				 * ext4 returns 0 for ENOTBLK
> +				 */
> +				struct ploop *ploop = pio->ploop;
> +
> +				PL_ERR("ret = 0 bi_size=%d\n", pio->bi_iter.bi_size);
> +				synchronize_rcu();
> +				ploop_queue_resubmit(pio);

Can this re-occur the second or third time? Should we limit how many 
times we can resubmit?

> +			}
> +
>   			if (pio->ret > 0) {
>   				ploop_pio_advance(pio, pio->ret);
>   				ploop_queue_resubmit(pio);
> -				return;
> -			} else {
> -				pio->bi_status = BLK_STS_IOERR;
> -				goto check_da;
>   			}
> +			return;
>   		}
>   		if (static_branch_unlikely(&ploop_standby_check))
>   			ploop_check_standby_mode(pio->ploop, pio->ret);
>   		pio->bi_status = errno_to_blk_status(pio->ret);
>   	}
> -check_da:
>   	if (pio->is_data_alloc) {
>   		completed = ploop_data_pio_end(pio);
>   		if (!completed)