Commit c337869d authored Jun 05, 2008 by Dan Williams Committed by Linus Torvalds Jun 06, 2008

md: do not compute parity unless it is on a failed drive



If a block is computed (rather than read) then a check/repair operation
may be lead to believe that the data on disk is correct, when infact it
isn't.  So only compute blocks for failed devices.

This issue has been around since at least 2.6.12, but has become harder to
hit in recent kernels since most reads bypass the cache.

echo repair > /sys/block/mdN/md/sync_action will set the parity blocks to the
correct state.

Cc: <stable@kernel.org>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent a6d8113a

drivers/md/raid5.c

+4 −1

Original line number	Diff line number	Diff line
		@@ -2002,6 +2002,7 @@ static int __handle_issuing_new_read_requests5(struct stripe_head *sh,
		* have quiesced.
		*/
		if ((s->uptodate == disks - 1) &&
		(s->failed && disk_idx == s->failed_num) &&
		!test_bit(STRIPE_OP_CHECK, &sh->ops.pending)) {
		set_bit(STRIPE_OP_COMPUTE_BLK, &sh->ops.pending);
		set_bit(R5_Wantcompute, &dev->flags);
		@@ -2087,7 +2088,9 @@ static void handle_issuing_new_read_requests6(struct stripe_head *sh,
		/* we would like to get this block, possibly
		* by computing it, but we might not be able to
		*/
		if (s->uptodate == disks-1) {
		if ((s->uptodate == disks - 1) &&
		(s->failed && (i == r6s->failed_num[0] \|\|
		i == r6s->failed_num[1]))) {
		pr_debug("Computing stripe %llu block %d\n",
		(unsigned long long)sh->sector, i);
		compute_block_1(sh, i, 0);

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