linux-stable-rt/drivers/md
K.Tanaka a07e6ab41b 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>
2008-03-04 16:35:18 -08:00
..
raid6test md: raid6: clean up the style of raid6test/test.c 2008-02-06 10:41:18 -08:00
.gitignore
Kconfig dm: targets no longer experimental 2008-02-08 02:10:32 +00:00
Makefile
bitmap.c md: reduce CPU wastage on idle md array with a write-intent bitmap 2008-03-04 16:35:17 -08:00
dm-bio-list.h
dm-bio-record.h
dm-crypt.c dm crypt: use async crypto 2008-02-08 02:11:14 +00:00
dm-delay.c
dm-emc.c
dm-exception-store.c dm snapshot: use uninitialized_var 2008-02-08 02:10:11 +00:00
dm-hw-handler.c
dm-hw-handler.h
dm-io.c
dm-io.h
dm-ioctl.c dm ioctl: use uninitialized_var 2008-02-08 02:10:16 +00:00
dm-linear.c
dm-log.c dm log: auto load modules 2008-02-08 02:11:19 +00:00
dm-log.h
dm-mpath-hp-sw.c
dm-mpath-rdac.c
dm-mpath.c dm mpath: add missing static 2008-02-08 02:10:35 +00:00
dm-mpath.h
dm-path-selector.c
dm-path-selector.h
dm-raid1.c dm-raid1.c: fix NULL dereferences 2008-02-19 15:52:27 -08:00
dm-round-robin.c
dm-snap.c dm snapshot: combine consecutive exceptions in memory 2008-02-08 02:11:27 +00:00
dm-snap.h dm snapshot: combine consecutive exceptions in memory 2008-02-08 02:11:27 +00:00
dm-stripe.c dm: stripe enhanced status return 2008-02-08 02:11:24 +00:00
dm-table.c Introduce path_put() 2008-02-14 21:13:33 -08:00
dm-target.c
dm-uevent.c
dm-uevent.h
dm-zero.c
dm.c dm: move deferred bio flushing to workqueue 2008-02-08 02:11:17 +00:00
dm.h dm: trigger change uevent on rename 2007-12-20 17:32:11 +00:00
faulty.c md: change ITERATE_RDEV to rdev_for_each 2008-02-06 10:41:19 -08:00
kcopyd.c
kcopyd.h
linear.c md: change ITERATE_RDEV to rdev_for_each 2008-02-06 10:41:19 -08:00
md.c md: lock access to rdev attributes properly 2008-03-04 16:35:18 -08:00
mktables.c md: raid6: Fix mktable.c 2008-02-06 10:41:18 -08:00
multipath.c md: change ITERATE_RDEV to rdev_for_each 2008-02-06 10:41:19 -08:00
raid0.c md: change ITERATE_RDEV to rdev_for_each 2008-02-06 10:41:19 -08:00
raid1.c md: fix possible raid1/raid10 deadlock on read error during resync 2008-03-04 16:35:18 -08:00
raid5.c md: fix an occasional deadlock in raid5 2008-02-06 10:41:19 -08:00
raid6.h
raid6algos.c
raid6altivec.uc
raid6int.uc
raid6mmx.c
raid6recov.c
raid6sse1.c
raid6sse2.c
raid6x86.h
raid10.c md: the md RAID10 resync thread could cause a md RAID10 array deadlock 2008-03-04 16:35:18 -08:00
unroll.pl