From: NeilBrown stripe_to_pdidx finds the index of the parity disk for a given stripe. It assumes raid5 in that it uses "disks-1" to determine the number of data disks. This is incorrect for raid6 but fortunately the two usages cancel each other out. The only way that 'data_disks' affects the calculation of pd_idx in raid5_compute_sector is when it is divided into the sector number. But as that sector number is calculated by multiplying in the wrong value of 'data_disks' the division produces the right value. So it is innocuous but needs to be fixed. Also change the calculation of raid_disks in compute_blocknr to make it more obviously correct (it seems at first to always use disks-1 too). Signed-off-by: Neil Brown Signed-off-by: Andrew Morton --- drivers/md/raid5.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff -puN drivers/md/raid5.c~md-fix-innocuous-bug-in-raid6-stripe_to_pdidx drivers/md/raid5.c --- a/drivers/md/raid5.c~md-fix-innocuous-bug-in-raid6-stripe_to_pdidx +++ a/drivers/md/raid5.c @@ -823,7 +823,8 @@ static sector_t raid5_compute_sector(sec static sector_t compute_blocknr(struct stripe_head *sh, int i) { raid5_conf_t *conf = sh->raid_conf; - int raid_disks = sh->disks, data_disks = raid_disks - 1; + int raid_disks = sh->disks; + int data_disks = raid_disks - conf->max_degraded; sector_t new_sector = sh->sector, check; int sectors_per_chunk = conf->chunk_size >> 9; sector_t stripe; @@ -859,7 +860,6 @@ static sector_t compute_blocknr(struct s } break; case 6: - data_disks = raid_disks - 2; if (i == raid6_next_disk(sh->pd_idx, raid_disks)) return 0; /* It is the Q disk */ switch (conf->algorithm) { @@ -1355,8 +1355,10 @@ static int stripe_to_pdidx(sector_t stri int pd_idx, dd_idx; int chunk_offset = sector_div(stripe, sectors_per_chunk); - raid5_compute_sector(stripe*(disks-1)*sectors_per_chunk - + chunk_offset, disks, disks-1, &dd_idx, &pd_idx, conf); + raid5_compute_sector(stripe * (disks - conf->max_degraded) + *sectors_per_chunk + chunk_offset, + disks, disks - conf->max_degraded, + &dd_idx, &pd_idx, conf); return pd_idx; } _