linux.git/drivers/md/raid10.c, branch v2.6.26-rc7

md: restart recovery cleanly after device failure.

2008-05-24T16:56:10+00:00

When we get any IO error during a recovery (rebuilding a spare), we abort
the recovery and restart it.

For RAID6 (and multi-drive RAID1) it may not be best to restart at the
beginning: when multiple failures can be tolerated, the recovery may be
able to continue and re-doing all that has already been done doesn't make
sense.

We already have the infrastructure to record where a recovery is up to
and restart from there, but it is not being used properly.
This is because:
  - We sometimes abort with MD_RECOVERY_ERR rather than just MD_RECOVERY_INTR,
    which causes the recovery not be be checkpointed.
  - We remove spares and then re-added them which loses important state
    information.

The distinction between MD_RECOVERY_ERR and MD_RECOVERY_INTR really isn't
needed.  If there is an error, the relevant drive will be marked as
Faulty, and that is enough to ensure correct handling of the error.  So we
first remove MD_RECOVERY_ERR, changing some of the uses of it to
MD_RECOVERY_INTR.

Then we cause the attempt to remove a non-faulty device from an array to
fail (unless recovery is impossible as the array is too degraded).  Then
when remove_and_add_spares attempts to remove the devices on which
recovery can continue, it will fail, they will remain in place, and
recovery will continue on them as desired.

Issue:  If we are halfway through rebuilding a spare and another drive
fails, and a new spare is immediately available,  do we want to:
 1/ complete the current rebuild, then go back and rebuild the new spare or
 2/ restart the rebuild from the start and rebuild both devices in
    parallel.

Both options can be argued for.  The code currently takes option 2 as
  a/ this requires least code change
  b/ this results in a minimally-degraded array in minimal time.

Cc: "Eivind Sarto" 
Signed-off-by: Neil Brown 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

Remove blkdev warning triggered by using md

2008-05-15T02:11:15+00:00

As setting and clearing queue flags now requires that we hold a spinlock
on the queue, and as blk_queue_stack_limits is called without that lock,
get the lock inside blk_queue_stack_limits.

For blk_queue_stack_limits to be able to find the right lock, each md
personality needs to set q->queue_lock to point to the appropriate lock.
Those personalities which didn't previously use a spin_lock, us
q->__queue_lock.  So always initialise that lock when allocated.

With this in place, setting/clearing of the QUEUE_FLAG_PLUGGED bit will no
longer cause warnings as it will be clear that the proper lock is held.

Thanks to Dan Williams for review and fixing the silly bugs.

Signed-off-by: NeilBrown 
Cc: Dan Williams 
Cc: Jens Axboe 
Cc: Alistair John Strachan 
Cc: Nick Piggin 
Cc: "Rafael J. Wysocki" 
Cc: Jacek Luczak 
Cc: Prakash Punnoor 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

misc: fix integer as NULL pointer warnings

2008-05-08T17:46:55+00:00

drivers/md/raid10.c:889:17: warning: Using plain integer as NULL pointer
drivers/media/video/cx18/cx18-driver.c:616:12: warning: Using plain integer as NULL pointer
sound/oss/kahlua.c:70:12: warning: Using plain integer as NULL pointer

Signed-off-by: Harvey Harrison 
Cc: Neil Brown 
Cc: Mauro Carvalho Chehab 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

md: support blocking writes to an array on device failure

2008-04-30T15:29:33+00:00

Allows a userspace metadata handler to take action upon detecting a device
failure.

Based on an original patch by Neil Brown.

Changes:
-added blocked_wait waitqueue to rdev
-don't qualify Blocked with Faulty always let userspace block writes
-added md_wait_for_blocked_rdev to wait for the block device to be clear, if
 userspace misses the notification another one is sent every 5 seconds
-set MD_RECOVERY_NEEDED after clearing "blocked"
-kill DoBlock flag, just test mddev->external

Signed-off-by: Dan Williams 
Signed-off-by: Neil Brown 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

raid: remove leading TAB on printk messages

2008-04-28T15:58:42+00:00

MD drivers use one printk() call to print 2 log messages and the second line
may be prefixed by a TAB character.  It may also output a trailing space
before newline.  klogd (I think) turns the TAB character into the 2 characters
'^I' when logging to a file.  This looks ugly.

Instead of a leading TAB to indicate continuation, prefix both output lines
with 'raid:' or similar.  Also remove any trailing space in the vicinity of
the affected code and consistently end the sentences with a period.

Signed-off-by: Nick Andrew 
Cc: Neil Brown 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

md: the md RAID10 resync thread could cause a md RAID10 array deadlock

2008-03-05T00:35:18+00:00

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 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

md: fix possible raid1/raid10 deadlock on read error during resync

2008-03-05T00:35:18+00:00

Thanks to K.Tanaka and the scsi fault injection framework, here is a fix for
another possible deadlock in raid1/raid10 error handing.

If a read request returns an error while a resync is happening and a resync
request is pending, the attempt to fix the error will block until the resync
progresses, and the resync will block until the read request completes.  Thus
a deadlock.

This patch fixes the problem.

Cc: "K.Tanaka" 
Signed-off-by: Neil Brown 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

md: don't attempt read-balancing for raid10 'far' layouts

2008-03-05T00:35:18+00:00

This patch changes the disk to be read for layout "far > 1" to always be the
disk with the lowest block address.

Thus the chunks to be read will always be (for a fully functioning array) from
the first band of stripes, and the raid will then work as a raid0 consisting
of the first band of stripes.

Some advantages:

The fastest part which is the outer sectors of the disks involved will be
used.  The outer blocks of a disk may be as much as 100 % faster than the
inner blocks.

Average seek time will be smaller, as seeks will always be confined to the
first part of the disks.

Mixed disks with different performance characteristics will work better, as
they will work as raid0, the sequential read rate will be number of disks
involved times the IO rate of the slowest disk.

If a disk is malfunctioning, the first disk which is working, and has the
lowest block address for the logical block will be used.

Signed-off-by: Keld Simonsen 
Signed-off-by: Neil Brown 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

md: fix deadlock in md/raid1 and md/raid10 when handling a read error

2008-03-05T00:35:17+00:00

When handling a read error, we freeze the array to stop any other IO while
attempting to over-write with correct data.

This is done in the raid1d(raid10d) thread and must wait for all submitted IO
to complete (except for requests that failed and are sitting in the retry
queue - these are counted in ->nr_queue and will stay there during a freeze).

However write requests need attention from raid1d as bitmap updates might be
required.  This can cause a deadlock as raid1 is waiting for requests to
finish that themselves need attention from raid1d.

So we create a new function 'flush_pending_writes' to give that attention, and
call it in freeze_array to be sure that we aren't waiting on raid1d.

Thanks to "K.Tanaka"  for finding and reporting this
problem.

Cc: "K.Tanaka" 
Signed-off-by: Neil Brown 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds

md: change ITERATE_RDEV to rdev_for_each

2008-02-06T18:41:19+00:00

As this is more in line with common practice in the kernel.  Also swap the
args around to be more like list_for_each.

Signed-off-by: Neil Brown 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds