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| author | K.Tanaka <k-tanaka@ce.jp.nec.com> | 2008-03-04 14:29:37 -0800 |
|---|---|---|
| committer | Linus Torvalds <torvalds@woody.linux-foundation.org> | 2008-03-04 16:35:18 -0800 |
| commit | a07e6ab41be179cf1ed728a4f41368435508b550 (patch) | |
| tree | 10773de394ab861259468372099c90b3f8671292 /drivers | |
| parent | 1c830532f6b44d10a1743ccd00e990c6b83396f5 (diff) | |
| download | linux-a07e6ab41be179cf1ed728a4f41368435508b550.tar.bz2 | |
md: the md RAID10 resync thread could cause a md RAID10 array deadlock
This message describes another issue about md RAID10 found by testing the
2.6.24 md RAID10 using new scsi fault injection framework.
Abstract:
When a scsi error results in disabling a disk during RAID10 recovery, the
resync threads of md RAID10 could stall.
This case, the raid array has already been broken and it may not matter. But
I think stall is not preferable. If it occurs, even shutdown or reboot will
fail because of resource busy.
The deadlock mechanism:
The r10bio_s structure has a "remaining" member to keep track of BIOs yet to
be handled when recovering. The "remaining" counter is incremented when
building a BIO in sync_request() and is decremented when finish a BIO in
end_sync_write().
If building a BIO fails for some reasons in sync_request(), the "remaining"
should be decremented if it has already been incremented. I found a case
where this decrement is forgotten. This causes a md_do_sync() deadlock
because md_do_sync() waits for md_done_sync() called by end_sync_write(), but
end_sync_write() never calls md_done_sync() because of the "remaining" counter
mismatch.
For example, this problem would be reproduced in the following case:
Personalities : [raid10]
md0 : active raid10 sdf1[4] sde1[5](F) sdd1[2] sdc1[1] sdb1[6](F)
3919616 blocks 64K chunks 2 near-copies [4/2] [_UU_]
[>....................] recovery = 2.2% (45376/1959808) finish=0.7min speed=45376K/sec
This case, sdf1 is recovering, sdb1 and sde1 are disabled.
An additional error with detaching sdd will cause a deadlock.
md0 : active raid10 sdf1[4] sde1[5](F) sdd1[6](F) sdc1[1] sdb1[7](F)
3919616 blocks 64K chunks 2 near-copies [4/1] [_U__]
[=>...................] recovery = 5.0% (99520/1959808) finish=5.9min speed=5237K/sec
2739 ? S< 0:17 [md0_raid10]
28608 ? D< 0:00 [md0_resync]
28629 pts/1 Ss 0:00 bash
28830 pts/1 R+ 0:00 ps ax
31819 ? D< 0:00 [kjournald]
The resync thread keeps working, but actually it is deadlocked.
Patch:
By this patch, the remaining counter will be decremented if needed.
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>
Diffstat (limited to 'drivers')
| -rw-r--r-- | drivers/md/raid10.c | 2 |
1 files changed, 2 insertions, 0 deletions
diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c index 8e5671d2f3d3..32389d2f18fc 100644 --- a/drivers/md/raid10.c +++ b/drivers/md/raid10.c @@ -1818,6 +1818,8 @@ static sector_t sync_request(mddev_t *mddev, sector_t sector_nr, int *skipped, i if (j == conf->copies) { /* Cannot recover, so abort the recovery */ put_buf(r10_bio); + if (rb2) + atomic_dec(&rb2->remaining); r10_bio = rb2; if (!test_and_set_bit(MD_RECOVERY_ERR, &mddev->recovery)) printk(KERN_INFO "raid10: %s: insufficient working devices for recovery.\n", |