[PATCH] md: fix innocuous bug in raid6 stripe_to_pdidx (b875e531) · Commits · 戴 / test

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 <neilb@suse.de> Signed-off-by:

Andrew Morton <akpm@osdl.org> Signed-off-by:

Linus Torvalds <torvalds@osdl.org>

drivers/md/raid5.c

+6 −4

Original line number	Diff line number	Diff line
		@@ -823,7 +823,8 @@ static sector_t raid5_compute_sector(sector_t r_sector, unsigned int raid_disks,
		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 stripe_head *sh, int i)
		}
		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 stripe, raid5_conf_t *conf, int disks)
		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;
		}

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