[Devel] [PATCH rh8] ploop: Update cached bat_entries before bio completion

[Kirill Tkhai]

https://jira.sw.ru/browse/PSBM-101499

On 19.02.2020 15:03, Kirill Tkhai wrote:
> Right after data_bio->end_io is called, it's expected
> a subsequent read returns written data. But there is
> a race between ploop_bat_write_complete() and ploop_map():
> 
> WRITE					READ
> ploop_bat_write_complete()
>   data_bio->end_io()
> 					write submitter sees write completion
> 					next submittion is READ
> 					ploop_map()
> 					  check BAT --- sees zero BAT entry
> 					  zero_fill_bio()
>   update BAT
> 
> So, the order has to be vise versa: first is to update BAT cache,
> second is to call data_bio->end_io().
> 
> https://jira.sw.ru/browse/PSBM-100788
> 
> Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
> ---
>  drivers/md/dm-ploop-map.c |   21 ++++++++++++---------
>  1 file changed, 12 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/md/dm-ploop-map.c b/drivers/md/dm-ploop-map.c
> index a67656b2b01e..4ca0f8e83400 100644
> --- a/drivers/md/dm-ploop-map.c
> +++ b/drivers/md/dm-ploop-map.c
> @@ -623,6 +623,18 @@ static void ploop_bat_write_complete(struct bio *bio)
>  
>  	track_bio(ploop, bio);
>  
> +	if (!bio->bi_status) {
> +		/*
> +		 * Success: now update local BAT copy. We could do this
> +		 * from our delayed work, but we want to publish new
> +		 * mapping in the fastest way. This must be done before
> +		 * data bios completion, since right after we complete
> +		 * a bio, subsequent read wants to see written data
> +		 * (ploop_map() wants to see not zero bat_entries[.]).
> +		 */
> +		ploop_advance_local_after_bat_wb(ploop, piwb, true);
> +	}
> +
>  	spin_lock_irqsave(&piwb->lock, flags);
>  	piwb->completed = true;
>  	piwb->bi_status = bio->bi_status;
> @@ -644,15 +656,6 @@ static void ploop_bat_write_complete(struct bio *bio)
>  		complete_cow(cow, bio->bi_status);
>  	}
>  
> -	if (!piwb->bi_status) {
> -		/*
> -		 * Success: now update local BAT copy. We could do this
> -		 * from our delayed work, but we want to publish new
> -		 * mapping in the fastest way.
> -		 */
> -		ploop_advance_local_after_bat_wb(ploop, piwb, true);
> -	}
> -
>  	/*
>  	 * In case of update BAT is failed, dst_clusters will be
>  	 * set back to holes_bitmap on last put_piwb().
> 
>