md/raid10: don't clear bitmap during recovery if array will still be degraded.

commit 18055569127253755d01733f6ecc004ed02f88d0 upstream.

If we have a raid10 with multiple missing devices, and we recover just
one of these to a spare, then we risk (depending on the bitmap and
array chunk size) clearing bits of the bitmap for which recovery isn't
complete (because a device is still missing).

This can lead to a subsequent "re-add" being recovered without
any IO happening, which would result in loss of data.

This patch takes the safe approach of not clearing bitmap bits
if the array will still be degraded.

This patch is suitable for all active -stable kernels.

Cc: stable@kernel.org
Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index dc50f98995165ea7a6fde2087b2ae2bcb3d7e9c6..b08dd95159f199e6398eddf65c1fe1bdf789a320 100644 (file)
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -1805,17 +1805,17 @@ static sector_t sync_request(mddev_t *mddev, sector_t sector_nr, int *skipped, i
                                r10_bio->sector = sect;
 
                                raid10_find_phys(conf, r10_bio);
-                               /* Need to check if this section will still be
+
+                               /* Need to check if the array will still be
                                 * degraded
                                 */
-                               for (j=0; j<conf->copies;j++) {
-                                       int d = r10_bio->devs[j].devnum;
-                                       if (conf->mirrors[d].rdev == NULL ||
-                                           test_bit(Faulty, &conf->mirrors[d].rdev->flags)) {
+                               for (j=0; j<conf->raid_disks; j++)
+                                       if (conf->mirrors[j].rdev == NULL ||
+                                           test_bit(Faulty, &conf->mirrors[j].rdev->flags)) {
                                                still_degraded = 1;
                                                break;
                                        }
-                               }
+
                                must_sync = bitmap_start_sync(mddev->bitmap, sect,
                                                              &sync_blocks, still_degraded);