kernel_optimize_test/include
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
..
acpi
asm-alpha [PATCH] tty: preparatory structures for termios revamp 2006-12-08 08:28:56 -08:00
asm-arm [PATCH] s3c2410fb: Add support for STN displays 2006-12-08 08:29:05 -08:00
asm-arm26 [PATCH] tty: preparatory structures for termios revamp 2006-12-08 08:28:56 -08:00
asm-avr32 [PATCH] tty: preparatory structures for termios revamp 2006-12-08 08:28:56 -08:00
asm-cris [PATCH] tty: preparatory structures for termios revamp 2006-12-08 08:28:56 -08:00
asm-frv [PATCH] tty: preparatory structures for termios revamp 2006-12-08 08:28:56 -08:00
asm-generic [PATCH] tty: switch to ktermios 2006-12-08 08:28:57 -08:00
asm-h8300 [PATCH] tty: preparatory structures for termios revamp 2006-12-08 08:28:56 -08:00
asm-i386 [PATCH] ide: more conversion to pci_get APIs 2006-12-08 08:29:03 -08:00
asm-ia64 [PATCH] tty: preparatory structures for termios revamp 2006-12-08 08:28:56 -08:00
asm-m32r [PATCH] tty: preparatory structures for termios revamp 2006-12-08 08:28:56 -08:00
asm-m68k [PATCH] tty: preparatory structures for termios revamp 2006-12-08 08:28:56 -08:00
asm-m68knommu [PATCH] cleanup asm/setup.h userspace visibility 2006-12-07 08:39:46 -08:00
asm-mips [PATCH] tty: preparatory structures for termios revamp 2006-12-08 08:28:56 -08:00
asm-parisc [PATCH] tty: preparatory structures for termios revamp 2006-12-08 08:28:56 -08:00
asm-powerpc [PATCH] tty: switch to ktermios 2006-12-08 08:28:57 -08:00
asm-ppc
asm-s390 [PATCH] tty: preparatory structures for termios revamp 2006-12-08 08:28:56 -08:00
asm-sh [PATCH] tty: preparatory structures for termios revamp 2006-12-08 08:28:56 -08:00
asm-sh64 [PATCH] cleanup asm/setup.h userspace visibility 2006-12-07 08:39:46 -08:00
asm-sparc [PATCH] tty: preparatory structures for termios revamp 2006-12-08 08:28:56 -08:00
asm-sparc64 [PATCH] tty: preparatory structures for termios revamp 2006-12-08 08:28:56 -08:00
asm-um [PATCH] UML: add generic BUG support 2006-12-08 08:28:39 -08:00
asm-v850 [PATCH] tty: preparatory structures for termios revamp 2006-12-08 08:28:56 -08:00
asm-x86_64 [PATCH] termios: Enable new style termios ioctls on x86-64 2006-12-08 08:28:57 -08:00
asm-xtensa [PATCH] Pass struct dev pointer to dma_cache_sync() 2006-12-07 08:39:41 -08:00
crypto
keys
linux [PATCH] dm: suspend: add noflush pushback 2006-12-08 08:29:09 -08:00
math-emu
media
mtd
net [PATCH] tty: switch to ktermios and new framework 2006-12-08 08:28:56 -08:00
pcmcia
rdma
rxrpc
scsi
sound
video [PATCH] video: pm3fb macros fix 2006-12-08 08:29:08 -08:00
Kbuild