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author | Kiyoshi Ueda <k-ueda@ct.jp.nec.com> | 2006-12-08 10:41:09 (GMT) |
---|---|---|
committer | Linus Torvalds <torvalds@woody.osdl.org> | 2006-12-08 16:29:09 (GMT) |
commit | 2e93ccc1933d08d32d9bde3784c3823e67b9b030 (patch) | |
tree | 1e8ad6a6444fc0a568e35f19628c89cdef9ad512 /drivers/md/dm.c | |
parent | 81fdb096dbcedcc3b94c7e47b59362b5214891e2 (diff) | |
download | linux-fsl-qoriq-2e93ccc1933d08d32d9bde3784c3823e67b9b030.tar.xz |
[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>
Diffstat (limited to 'drivers/md/dm.c')
-rw-r--r-- | drivers/md/dm.c | 105 |
1 files changed, 95 insertions, 10 deletions
diff --git a/drivers/md/dm.c b/drivers/md/dm.c index d8544e1..fe7c56e 100644 --- a/drivers/md/dm.c +++ b/drivers/md/dm.c @@ -68,10 +68,12 @@ union map_info *dm_get_mapinfo(struct bio *bio) #define DMF_FROZEN 2 #define DMF_FREEING 3 #define DMF_DELETING 4 +#define DMF_NOFLUSH_SUSPENDING 5 struct mapped_device { struct rw_semaphore io_lock; struct semaphore suspend_lock; + spinlock_t pushback_lock; rwlock_t map_lock; atomic_t holders; atomic_t open_count; @@ -90,6 +92,7 @@ struct mapped_device { atomic_t pending; wait_queue_head_t wait; struct bio_list deferred; + struct bio_list pushback; /* * The current mapping. @@ -444,23 +447,50 @@ int dm_set_geometry(struct mapped_device *md, struct hd_geometry *geo) * you this clearly demarcated crap. *---------------------------------------------------------------*/ +static int __noflush_suspending(struct mapped_device *md) +{ + return test_bit(DMF_NOFLUSH_SUSPENDING, &md->flags); +} + /* * Decrements the number of outstanding ios that a bio has been * cloned into, completing the original io if necc. */ static void dec_pending(struct dm_io *io, int error) { - if (error) + unsigned long flags; + + /* Push-back supersedes any I/O errors */ + if (error && !(io->error > 0 && __noflush_suspending(io->md))) io->error = error; if (atomic_dec_and_test(&io->io_count)) { + if (io->error == DM_ENDIO_REQUEUE) { + /* + * Target requested pushing back the I/O. + * This must be handled before the sleeper on + * suspend queue merges the pushback list. + */ + spin_lock_irqsave(&io->md->pushback_lock, flags); + if (__noflush_suspending(io->md)) + bio_list_add(&io->md->pushback, io->bio); + else + /* noflush suspend was interrupted. */ + io->error = -EIO; + spin_unlock_irqrestore(&io->md->pushback_lock, flags); + } + if (end_io_acct(io)) /* nudge anyone waiting on suspend queue */ wake_up(&io->md->wait); - blk_add_trace_bio(io->md->queue, io->bio, BLK_TA_COMPLETE); + if (io->error != DM_ENDIO_REQUEUE) { + blk_add_trace_bio(io->md->queue, io->bio, + BLK_TA_COMPLETE); + + bio_endio(io->bio, io->bio->bi_size, io->error); + } - bio_endio(io->bio, io->bio->bi_size, io->error); free_io(io->md, io); } } @@ -480,7 +510,11 @@ static int clone_endio(struct bio *bio, unsigned int done, int error) if (endio) { r = endio(tio->ti, bio, error, &tio->info); - if (r < 0) + if (r < 0 || r == DM_ENDIO_REQUEUE) + /* + * error and requeue request are handled + * in dec_pending(). + */ error = r; else if (r == DM_ENDIO_INCOMPLETE) /* The target will handle the io */ @@ -554,8 +588,8 @@ static void __map_bio(struct dm_target *ti, struct bio *clone, clone->bi_sector); generic_make_request(clone); - } else if (r < 0) { - /* error the io and bail out */ + } else if (r < 0 || r == DM_MAPIO_REQUEUE) { + /* error the io and bail out, or requeue it if needed */ md = tio->io->md; dec_pending(tio->io, r); /* @@ -952,6 +986,7 @@ static struct mapped_device *alloc_dev(int minor) memset(md, 0, sizeof(*md)); init_rwsem(&md->io_lock); init_MUTEX(&md->suspend_lock); + spin_lock_init(&md->pushback_lock); rwlock_init(&md->map_lock); atomic_set(&md->holders, 1); atomic_set(&md->open_count, 0); @@ -1282,10 +1317,12 @@ static void unlock_fs(struct mapped_device *md) int dm_suspend(struct mapped_device *md, unsigned suspend_flags) { struct dm_table *map = NULL; + unsigned long flags; DECLARE_WAITQUEUE(wait, current); struct bio *def; int r = -EINVAL; int do_lockfs = suspend_flags & DM_SUSPEND_LOCKFS_FLAG ? 1 : 0; + int noflush = suspend_flags & DM_SUSPEND_NOFLUSH_FLAG ? 1 : 0; down(&md->suspend_lock); @@ -1294,6 +1331,13 @@ int dm_suspend(struct mapped_device *md, unsigned suspend_flags) map = dm_get_table(md); + /* + * DMF_NOFLUSH_SUSPENDING must be set before presuspend. + * This flag is cleared before dm_suspend returns. + */ + if (noflush) + set_bit(DMF_NOFLUSH_SUSPENDING, &md->flags); + /* This does not get reverted if there's an error later. */ dm_table_presuspend_targets(map); @@ -1301,11 +1345,14 @@ int dm_suspend(struct mapped_device *md, unsigned suspend_flags) if (!md->suspended_bdev) { DMWARN("bdget failed in dm_suspend"); r = -ENOMEM; - goto out; + goto flush_and_out; } - /* Flush I/O to the device. */ - if (do_lockfs) { + /* + * Flush I/O to the device. + * noflush supersedes do_lockfs, because lock_fs() needs to flush I/Os. + */ + if (do_lockfs && !noflush) { r = lock_fs(md); if (r) goto out; @@ -1341,6 +1388,14 @@ int dm_suspend(struct mapped_device *md, unsigned suspend_flags) down_write(&md->io_lock); remove_wait_queue(&md->wait, &wait); + if (noflush) { + spin_lock_irqsave(&md->pushback_lock, flags); + clear_bit(DMF_NOFLUSH_SUSPENDING, &md->flags); + bio_list_merge_head(&md->deferred, &md->pushback); + bio_list_init(&md->pushback); + spin_unlock_irqrestore(&md->pushback_lock, flags); + } + /* were we interrupted ? */ r = -EINTR; if (atomic_read(&md->pending)) { @@ -1349,7 +1404,7 @@ int dm_suspend(struct mapped_device *md, unsigned suspend_flags) __flush_deferred_io(md, def); up_write(&md->io_lock); unlock_fs(md); - goto out; + goto out; /* pushback list is already flushed, so skip flush */ } up_write(&md->io_lock); @@ -1359,6 +1414,25 @@ int dm_suspend(struct mapped_device *md, unsigned suspend_flags) r = 0; +flush_and_out: + if (r && noflush) { + /* + * Because there may be already I/Os in the pushback list, + * flush them before return. + */ + down_write(&md->io_lock); + + spin_lock_irqsave(&md->pushback_lock, flags); + clear_bit(DMF_NOFLUSH_SUSPENDING, &md->flags); + bio_list_merge_head(&md->deferred, &md->pushback); + bio_list_init(&md->pushback); + spin_unlock_irqrestore(&md->pushback_lock, flags); + + def = bio_list_get(&md->deferred); + __flush_deferred_io(md, def); + up_write(&md->io_lock); + } + out: if (r && md->suspended_bdev) { bdput(md->suspended_bdev); @@ -1445,6 +1519,17 @@ int dm_suspended(struct mapped_device *md) return test_bit(DMF_SUSPENDED, &md->flags); } +int dm_noflush_suspending(struct dm_target *ti) +{ + struct mapped_device *md = dm_table_get_md(ti->table); + int r = __noflush_suspending(md); + + dm_put(md); + + return r; +} +EXPORT_SYMBOL_GPL(dm_noflush_suspending); + static struct block_device_operations dm_blk_dops = { .open = dm_blk_open, .release = dm_blk_close, |