linux/drivers/md
Kiyoshi Ueda 2e93ccc193 [PATCH] dm: suspend: add noflush pushback
In device-mapper I/O is sometimes queued within targets for later processing.
For example the multipath target can be configured to store I/O when no paths
are available instead of returning it -EIO.

This patch allows the device-mapper core to instruct a target to transfer the
contents of any such in-target queue back into the core.  This frees up the
resources used by the target so the core can replace that target with an
alternative one and then resend the I/O to it.  Without this patch the only
way to change the target in such circumstances involves returning the I/O with
an error back to the filesystem/application.  In the multipath case, this
patch will let us add new paths for existing I/O to try after all the existing
paths have failed.

    DMF_NOFLUSH_SUSPENDING
    ----------------------

If the DM_NOFLUSH_FLAG ioctl option is specified at suspend time, the
DMF_NOFLUSH_SUSPENDING flag is set in md->flags during dm_suspend().  It
is always cleared before dm_suspend() returns.

The flag must be visible while the target is flushing pending I/Os so it
is set before presuspend where the flush starts and unset after the wait
for md->pending where the flush ends.

Target drivers can check this flag by calling dm_noflush_suspending().

    DM_MAPIO_REQUEUE / DM_ENDIO_REQUEUE
    -----------------------------------

A target's map() function can now return DM_MAPIO_REQUEUE to request the
device mapper core queue the bio.

Similarly, a target's end_io() function can return DM_ENDIO_REQUEUE to request
the same.  This has been labelled 'pushback'.

The __map_bio() and clone_endio() functions in the core treat these return
values as errors and call dec_pending() to end the I/O.

    dec_pending
    -----------

dec_pending() saves the pushback request in struct dm_io->error.  Once all
the split clones have ended, dec_pending() will put the original bio on
the md->pushback list.  Note that this supercedes any I/O errors.

It is possible for the suspend with DM_NOFLUSH_FLAG to be aborted while
in progress (e.g. by user interrupt).  dec_pending() checks for this and
returns -EIO if it happened.

    pushdback list and pushback_lock
    --------------------------------

The bio is queued on md->pushback temporarily in dec_pending(), and after
all pending I/Os return, md->pushback is merged into md->deferred in
dm_suspend() for re-issuing at resume time.

md->pushback_lock protects md->pushback.
The lock should be held with irq disabled because dec_pending() can be
called from interrupt context.

Queueing bios to md->pushback in dec_pending() must be done atomically
with the check for DMF_NOFLUSH_SUSPENDING flag.  So md->pushback_lock is
held when checking the flag.  Otherwise dec_pending() may queue a bio to
md->pushback after the interrupted dm_suspend() flushes md->pushback.
Then the bio would be left in md->pushback.

Flag setting in dm_suspend() can be done without md->pushback_lock because
the flag is checked only after presuspend and the set value is already
made visible via the target's presuspend function.

The flag can be checked without md->pushback_lock (e.g. the first part of
the dec_pending() or target drivers), because the flag is checked again
with md->pushback_lock held when the bio is really queued to md->pushback
as described above.  So even if the flag is cleared after the lockless
checkings, the bio isn't left in md->pushback but returned to applications
with -EIO.

    Other notes on the current patch
    --------------------------------

- md->pushback is added to the struct mapped_device instead of using
  md->deferred directly because md->io_lock which protects md->deferred is
  rw_semaphore and can't be used in interrupt context like dec_pending(),
  and md->io_lock protects the DMF_BLOCK_IO flag of md->flags too.

- Don't issue lock_fs() in dm_suspend() if the DM_NOFLUSH_FLAG
  ioctl option is specified, because I/Os generated by lock_fs() would be
  pushed back and never return if there were no valid devices.

- If an error occurs in dm_suspend() after the DMF_NOFLUSH_SUSPENDING
  flag is set, md->pushback must be flushed because I/Os may be queued to
  the list already.  (flush_and_out label in dm_suspend())

    Test results
    ------------

I have tested using multipath target with the next patch.

The following tests are for regression/compatibility:
  - I/Os succeed when valid paths exist;
  - I/Os fail when there are no valid paths and queue_if_no_path is not
    set;
  - I/Os are queued in the multipath target when there are no valid paths and
    queue_if_no_path is set;
  - The queued I/Os above fail when suspend is issued without the
    DM_NOFLUSH_FLAG ioctl option.  I/Os spanning 2 multipath targets also
    fail.

The following tests are for the normal code path of new pushback feature:
  - Queued I/Os in the multipath target are flushed from the target
    but don't return when suspend is issued with the DM_NOFLUSH_FLAG
    ioctl option;
  - The I/Os above are queued in the multipath target again when
    resume is issued without path recovery;
  - The I/Os above succeed when resume is issued after path recovery
    or table load;
  - Queued I/Os in the multipath target succeed when resume is issued
    with the DM_NOFLUSH_FLAG ioctl option after table load. I/Os
    spanning 2 multipath targets also succeed.

The following tests are for the error paths of the new pushback feature:
  - When the bdget_disk() fails in dm_suspend(), the
    DMF_NOFLUSH_SUSPENDING flag is cleared and I/Os already queued to the
    pushback list are flushed properly.
  - When suspend with the DM_NOFLUSH_FLAG ioctl option is interrupted,
      o I/Os which had already been queued to the pushback list
        at the time don't return, and are re-issued at resume time;
      o I/Os which hadn't been returned at the time return with EIO.

Signed-off-by: Kiyoshi Ueda <k-ueda@ct.jp.nec.com>
Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Cc: dm-devel@redhat.com
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
2006-12-08 08:29:09 -08:00
..
raid6test [PATCH] RAID6 Altivec fix 2005-09-17 11:49:58 -07:00
.gitignore gitignore: misc files 2006-01-01 22:21:50 +01:00
bitmap.c [PATCH] struct path: convert md 2006-12-08 08:28:47 -08:00
dm-bio-list.h [PATCH] dm: suspend: add noflush pushback 2006-12-08 08:29:09 -08:00
dm-bio-record.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
dm-crypt.c [PATCH] dm: map and endio symbolic return codes 2006-12-08 08:29:09 -08:00
dm-emc.c [PATCH] struct path: rename DM's struct path 2006-12-08 08:28:40 -08:00
dm-exception-store.c [PATCH] dm snapshot: fix metadata writing when suspending 2006-10-03 08:04:14 -07:00
dm-hw-handler.c BUG_ON() Conversion in md/dm-hw-handler.c 2006-03-24 18:36:27 +01:00
dm-hw-handler.h [PATCH] struct path: rename DM's struct path 2006-12-08 08:28:40 -08:00
dm-io.c [PATCH] dm io: fix bi_max_vecs 2006-12-08 08:29:08 -08:00
dm-io.h [PATCH] device-mapper: remove unused definition 2006-01-06 08:34:00 -08:00
dm-ioctl.c [PATCH] dm: ioctl: add noflush suspend 2006-12-08 08:29:09 -08:00
dm-linear.c [PATCH] dm: map and endio symbolic return codes 2006-12-08 08:29:09 -08:00
dm-log.c [PATCH] dm: improve error message consistency 2006-06-26 09:58:36 -07:00
dm-log.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
dm-mpath.c [PATCH] dm: map and endio symbolic return codes 2006-12-08 08:29:09 -08:00
dm-mpath.h [PATCH] struct path: rename DM's struct path 2006-12-08 08:28:40 -08:00
dm-path-selector.c BUG_ON() Conversion in md/dm-path-selector.c 2006-03-26 18:21:58 +02:00
dm-path-selector.h [PATCH] struct path: rename DM's struct path 2006-12-08 08:28:40 -08:00
dm-raid1.c [PATCH] dm: map and endio symbolic return codes 2006-12-08 08:29:09 -08:00
dm-round-robin.c [PATCH] struct path: rename DM's struct path 2006-12-08 08:28:40 -08:00
dm-snap.c [PATCH] dm: map and endio symbolic return codes 2006-12-08 08:29:09 -08:00
dm-snap.h [PATCH] dm snapshot: add workqueue 2006-10-03 08:04:14 -07:00
dm-stripe.c [PATCH] dm: map and endio symbolic return codes 2006-12-08 08:29:09 -08:00
dm-table.c [PATCH] dm table: add target flush 2006-10-03 08:04:16 -07:00
dm-target.c [PATCH] dm: improve error message consistency 2006-06-26 09:58:36 -07:00
dm-zero.c [PATCH] dm: map and endio symbolic return codes 2006-12-08 08:29:09 -08:00
dm.c [PATCH] dm: suspend: add noflush pushback 2006-12-08 08:29:09 -08:00
dm.h [PATCH] dm: suspend: add noflush pushback 2006-12-08 08:29:09 -08:00
faulty.c [PATCH] md: allow array level to be set textually via sysfs 2006-01-06 08:34:09 -08:00
Kconfig [PATCH] md: remove 'experimental' classification from raid5 reshape 2006-10-03 08:04:18 -07:00
kcopyd.c [PATCH] slab: remove kmem_cache_t 2006-12-07 08:39:25 -08:00
kcopyd.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
linear.c [PATCH] md: define backing_dev_info.congested_fn for raid0 and linear 2006-10-03 08:04:18 -07:00
Makefile [PATCH] md: merge raid5 and raid6 code 2006-06-26 09:58:37 -07:00
md.c [PATCH] struct path: convert md 2006-12-08 08:28:47 -08:00
mktables.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
multipath.c [PATCH] md: fix up maintenance of ->degraded in multipath 2006-10-28 11:30:51 -07:00
raid0.c [PATCH] md: define backing_dev_info.congested_fn for raid0 and linear 2006-10-03 08:04:18 -07:00
raid1.c [PATCH] md: fix printk format warnings, seen on powerpc64: 2006-10-28 11:30:52 -07:00
raid5.c [PATCH] slab: remove kmem_cache_t 2006-12-07 08:39:25 -08:00
raid6.h [PATCH] RAID6 Altivec fix 2005-09-17 11:49:58 -07:00
raid6algos.c [PATCH] drivers/md/raid6algos.c: fix a NULL dereference 2006-06-23 07:43:08 -07:00
raid6altivec.uc [PATCH] RAID6 Altivec fix 2005-09-17 11:49:58 -07:00
raid6int.uc Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
raid6mmx.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
raid6recov.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
raid6sse1.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
raid6sse2.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
raid6x86.h Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
raid10.c [PATCH] md: fix printk format warnings, seen on powerpc64: 2006-10-28 11:30:52 -07:00
unroll.pl Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00
xor.c Linux-2.6.12-rc2 2005-04-16 15:20:36 -07:00