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authorJun'ichi Nomura <j-nomura@ce.jp.nec.com>2006-03-27 01:17:47 -0800
committerLinus Torvalds <torvalds@g5.osdl.org>2006-03-27 08:44:58 -0800
commit930d332a23682202c07df0276dd665a57755b37d (patch)
tree0a0202fb581a65a0b63a4a98aa725eb2088a7814 /drivers/md/dm-raid1.c
parent76df1c651b66bdf07d60b3d60789feb5f58d73e3 (diff)
[PATCH] drivers/md/dm-raid1.c: Fix inconsistent mirroring after interrupted recovery
dm-mirror has potential data corruption problem: while on-disk log shows that all disk contents are in-sync, actual contents of the disks are not synchronized. This problem occurs if initial recovery (synching) is interrupted and resumed. Attached patch fixes this problem. Background: rh_dec() changes the region state from RH_NOSYNC (out-of-sync) to RH_CLEAN (in-sync), which results in the corresponding bit of clean_bits being set. This is harmful if on-disk log is used and the map is removed/suspended before the initial sync is completed. The clean_bits is written down to the on-disk log at the map removal, and, upon resume, it's read and copied to sync_bits. Since the recovery process refers to the sync_bits to find a region to be recovered, the region whose state was changed from RH_NOSYNC to RH_CLEAN is no longer recovered. If you haven't applied dm-raid1-read-balancing.patch proposed in dm-devel sometimes ago, the contents of the mirrored disk just corrupt silently. If you have, balanced read may get bogus data from out-of-sync disks. The patch keeps RH_NOSYNC state unchanged. It will be changed to RH_RECOVERING when recovery starts and get reclaimed when the recovery completes. So it doesn't leak the region hash entry. Description: Keep RH_NOSYNC state unchanged when I/O on the region completes. rh_dec() changes the region state from RH_NOSYNC (out-of-sync) to RH_CLEAN (in-sync), which results in the corresponding bit of clean_bits being set. This is harmful if on-disk log is used and the map is removed/suspended before the initial sync is completed. The clean_bits is written down to the on-disk log at the map removal, and, upon resume, it's read and copied to sync_bits. Since the recovery process refers to the sync_bits to find a region to be recovered, the region whose state was changed from RH_NOSYNC to RH_CLEAN is no longer recovered. If you haven't applied dm-raid1-read-balancing.patch proposed in dm-devel sometimes ago, the contents of the mirrored disk just corrupt silently. If you have, balanced read may get bogus data from out-of-sync disks. The RH_NOSYNC region will be changed to RH_RECOVERING when recovery starts on the region and get reclaimed when the recovery completes. So it doesn't leak the region hash entry. Alasdair said: I've analysed the relevant part of the state machine and I believe that the patch is correct. (Further work on this code is still needed - this patch has the side-effect of holding onto memory unnecessarily for long periods of time under certain workloads - but better that than corrupting data.) Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com> Acked-by: Alasdair G Kergon <agk@redhat.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'drivers/md/dm-raid1.c')
-rw-r--r--drivers/md/dm-raid1.c14
1 files changed, 13 insertions, 1 deletions
diff --git a/drivers/md/dm-raid1.c b/drivers/md/dm-raid1.c
index 4e90f231fbfb..3d90f1b37e08 100644
--- a/drivers/md/dm-raid1.c
+++ b/drivers/md/dm-raid1.c
@@ -402,9 +402,21 @@ static void rh_dec(struct region_hash *rh, region_t region)
spin_lock_irqsave(&rh->region_lock, flags);
if (atomic_dec_and_test(&reg->pending)) {
+ /*
+ * There is no pending I/O for this region.
+ * We can move the region to corresponding list for next action.
+ * At this point, the region is not yet connected to any list.
+ *
+ * If the state is RH_NOSYNC, the region should be kept off
+ * from clean list.
+ * The hash entry for RH_NOSYNC will remain in memory
+ * until the region is recovered or the map is reloaded.
+ */
+
+ /* do nothing for RH_NOSYNC */
if (reg->state == RH_RECOVERING) {
list_add_tail(&reg->list, &rh->quiesced_regions);
- } else {
+ } else if (reg->state == RH_DIRTY) {
reg->state = RH_CLEAN;
list_add(&reg->list, &rh->clean_regions);
}