On 06/29/2014 10:40 PM, NeilBrown wrote:
On Mon, 30 Jun 2014 13:23:35 +1000 NeilBrown <neilb@xxxxxxx> wrote:
On Sat, 28 Jun 2014 18:43:00 -0500 Bill <billstuff2001@xxxxxxxxxxxxx> wrote:
On 06/22/2014 08:36 PM, NeilBrown wrote:
On Sat, 21 Jun 2014 00:31:39 -0500 Bill<billstuff2001@xxxxxxxxxxxxx> wrote:
Hi Neil,
I'm running a test on 3.14.8 and seeing data corruption after a recovery.
I have this array:
md5 : active raid5 sdc1[2] sdb1[1] sda1[0] sde1[4] sdd1[3]
16777216 blocks level 5, 64k chunk, algorithm 2 [5/5] [UUUUU]
bitmap: 0/1 pages [0KB], 2048KB chunk
with an xfs filesystem on it:
/dev/md5 on /hdtv/data5 type xfs
(rw,noatime,barrier,swalloc,allocsize=256m,logbsize=256k,largeio)
and I do this in a loop:
1. start writing 1/4 GB files to the filesystem
2. fail a disk. wait a bit
3. remove it. wait a bit
4. add the disk back into the array
5. wait for the array to sync and the file writes to finish
6. checksum the files.
7. wait a bit and do it all again
The checksum QC will eventually fail, usually after a few hours.
My last test failed after 4 hours:
18:51:48 - mdadm /dev/md5 -f /dev/sdc1
18:51:58 - mdadm /dev/md5 -r /dev/sdc1
18:52:06 - start writing 3 files
18:52:08 - mdadm /dev/md5 -a /dev/sdc1
18:52:18 - array recovery done
18:52:23 - writes finished. QC failed for one of three files.
dmesg shows no errors and the disks are operating normally.
If I "check" /dev/md5 it shows mismatch_cnt = 896
If I dump the raw data on sd[abcde]1 underneath the bad file, it shows
sd[abde]1 are correct, and sdc1 has some chunks of old data from a
previous file.
If I fail sdc1, --zero-superblock it, and add it, it then syncs and the
QC is correct.
So somehow is seems like md is loosing track of some changes which need
to be
written to sdc1 in the recovery. But rarely - in this case it failed
after 175 cycles.
Do you have any idea what could be happening here?
No. As you say, it looks like md is not setting a bit in the bitmap
correctly, or ignoring one that is set, or maybe clearing one that shouldn't
be cleared.
The last is most likely I would guess.
Neil,
I'm still digging through this but I found something that might help
narrow it
down - the bitmap stays dirty after the re-add and recovery is complete:
Filename : /dev/sde1
Magic : 6d746962
Version : 4
UUID : 609846f8:ad08275f:824b3cb4:2e180e57
Events : 5259
Events Cleared : 5259
State : OK
Chunksize : 2 MB
Daemon : 5s flush period
Write Mode : Normal
Sync Size : 4194304 (4.00 GiB 4.29 GB)
Bitmap : 2048 bits (chunks), 2 dirty (0.1%)
^^^^^^^^^^^^^^
This is after 1/2 hour idle. sde1 was the one removed / re-added, but
all five disks show the same bitmap info, and the event count matches
that of
the array (5259). At this point the QC check fails.
Then I manually failed, removed and re-added /dev/sde1, and shortly the
array
synced the dirty chunks:
Filename : /dev/sde1
Magic : 6d746962
Version : 4
UUID : 609846f8:ad08275f:824b3cb4:2e180e57
Events : 5275
Events Cleared : 5259
State : OK
Chunksize : 2 MB
Daemon : 5s flush period
Write Mode : Normal
Sync Size : 4194304 (4.00 GiB 4.29 GB)
Bitmap : 2048 bits (chunks), 0 dirty (0.0%)
^^^^^^^^^^^^^^
Now the QC check succeeds and an array "check" shows no mismatches.
So it seems like md is ignoring a set bit in the bitmap, which then gets
noticed
with the fail / remove / re-add sequence.
Thanks, that helps a lot ... maybe.
I have a theory. This patch explains it and should fix it.
I'm not sure this is the patch I will go with if it works, but it will help
confirm my theory.
Can you test it?
thanks,
NeilBrown
diff --git a/drivers/md/md.c b/drivers/md/md.c
index 34846856dbc6..27387a3740c8 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -7906,6 +7906,15 @@ void md_check_recovery(struct mddev *mddev)
clear_bit(MD_RECOVERY_CHECK, &mddev->recovery);
clear_bit(MD_RECOVERY_REQUESTED, &mddev->recovery);
set_bit(MD_RECOVERY_RECOVER, &mddev->recovery);
+ /* If there is a bitmap, we need to make sure
+ * all writes that started before we added a spare
+ * complete before we start doing a recovery.
+ * Otherwise the write might complete and set
+ * a bit in the bitmap after the recovery has
+ * checked that bit and skipped that region.
+ */
+ mddev->pers->quiesce(mddev, 1);
+ mddev->pers->quiesce(mddev, 0);
} else if (mddev->recovery_cp < MaxSector) {
set_bit(MD_RECOVERY_SYNC, &mddev->recovery);
clear_bit(MD_RECOVERY_RECOVER, &mddev->recovery);
Don't even bother trying that - it will definitely deadlock.
Please try this instead.
NeilBrown
diff --git a/drivers/md/md.c b/drivers/md/md.c
index 34846856dbc6..f8cd0bd83402 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -7501,6 +7501,16 @@ void md_do_sync(struct md_thread *thread)
rdev->recovery_offset < j)
j = rdev->recovery_offset;
rcu_read_unlock();
+
+ /* If there is a bitmap, we need to make sure
+ * all writes that started before we added a spare
+ * complete before we start doing a recovery.
+ * Otherwise the write might complete and set
+ * a bit in the bitmap after the recovery has
+ * checked that bit and skipped that region.
+ */
+ mddev->pers->quiesce(mddev, 1);
+ mddev->pers->quiesce(mddev, 0);
}
printk(KERN_INFO "md: %s of RAID array %s\n", desc, mdname(mddev));
My recent tests all failed within an hour, and with this patch it's still
running after 24 hours, so it looks promising. I'll leave it running and let
you know if anything bad happens.
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