Re: [PATCH 1/3] md/raid10: restore still_degraded detection in recovery

Dear Mykola,


Thank you for your patch.

Am 19.07.26 um 16:42 schrieb Mykola Marzhan:
> raid10_sync_request()'s recovery arm passes still_degraded -- "will
> the array still be degraded after this recovery completes?" -- to
> md_bitmap_start_sync(), whose !degraded branch consumes the chunk's
> NEEDED marker, the write-intent record.  That is only safe when the
> recovery restores full redundancy; otherwise the record still
> describes writes an absent member missed.
> 
> Commit fe6a19d40ceb ("md/md-bitmap: merge md_bitmap_start_sync()
> into bitmap_operations") turned the detection loop's only assignment
> from "still_degraded = 1" into "still_degraded = false" in its
> int-to-bool styling pass, so the flag has been constant false ever
> since.  raid1 and raid5 were converted to "= true"; only raid10 was
> inverted.
> 
> The result is silent data loss on a classic-bitmap raid10 that stays
> degraded across a recovery.  With mirror pairs {A,B} and {C,D}: lose
> D, keep writing, lose B, add a spare.  The rebuild into B's slot
> strips NEEDED from every chunk -- including chunks whose only
> unsatisfied intent belonged to D -- so a later --re-add of D sees an
> empty intent record, completes instantly, and serves stale data.
> 
> Restore the pre-conversion assignment.  Only the classic-bitmap
> recovery arm is affected: llbitmap ignores the degraded parameter,
> and the resync arm passes mddev->degraded directly.
> 
> Fixes: fe6a19d40ceb ("md/md-bitmap: merge md_bitmap_start_sync() into bitmap_operations")
> Cc: [email protected] # v6.12+
> Assisted-by: Claude-Code:claude-opus-4-8
> Signed-off-by: Mykola Marzhan <[email protected]>
> ---
>   drivers/md/raid10.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
> index 0a3cfdd3f5df..54cddb3a98cd 100644
> --- a/drivers/md/raid10.c
> +++ b/drivers/md/raid10.c
> @@ -3365,7 +3365,7 @@ static sector_t raid10_sync_request(struct mddev *mddev, sector_t sector_nr,
>   				struct md_rdev *rdev = conf->mirrors[j].rdev;
>   
>   				if (rdev == NULL || test_bit(Faulty, &rdev->flags)) {
> -					still_degraded = false;
> +					still_degraded = true;
>   					break;
>   				}
>   			}

Reviewed-by: Paul Menzel <[email protected]>


Kind regards,

Paul