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Re: [dm-devel] [PATCH 23/41] dm: implement REQ_FLUSH/FUA support for bio-based dm



I quite disagree with the patch. It changes too many things.

What I said and what I want to see:

Take dm code as is. Treat FLUSH requests as empty barriers.


So I want to see a patch that only changes:

bio_empty_barrier(bio)  ->  bio->bi_rw & REQ_FLUSH
WRITE_BARRIER -> WRITE_FLUSH
etc.

so that the code compiles and works.

DON'T CHANGE ANYTHING ELSE.

Requirements of flushes are subset of requirements of barriers, so if you 
send flush and it is treated as a barrier inside DM, there's no problem. 
DM code that I wrote only sends out zero-data barriers and already treats 
them as flushes (it doesn't rely on ordering), so there's no problem with 
sent requests too.

Once fluges get into kernel, I'll clean it up to allow parallel flushes 
and requests, etc. But not before. I don't want to work on an interface 
that is under development and may be changed.

Mikulas



On Fri, 3 Sep 2010, Tejun Heo wrote:

> This patch converts bio-based dm to support REQ_FLUSH/FUA instead of
> now deprecated REQ_HARDBARRIER.
> 
> * -EOPNOTSUPP handling logic dropped.
> 
> * Preflush is handled as before but postflush is dropped and replaced
>   with passing down REQ_FUA to member request_queues.  This replaces
>   one array wide cache flush w/ member specific FUA writes.
> 
> * __split_and_process_bio() now calls __clone_and_map_flush() directly
>   for flushes and guarantees all FLUSH bio's going to targets are zero
> `  length.
> 
> * It's now guaranteed that all FLUSH bio's which are passed onto dm
>   targets are zero length.  bio_empty_barrier() tests are replaced
>   with REQ_FLUSH tests.
> 
> * Empty WRITE_BARRIERs are replaced with WRITE_FLUSHes.
> 
> * Dropped unlikely() around REQ_FLUSH tests.  Flushes are not unlikely
>   enough to be marked with unlikely().
> 
> * Block layer now filters out REQ_FLUSH/FUA bio's if the request_queue
>   doesn't support cache flushing.  Advertise REQ_FLUSH | REQ_FUA
>   capability.
> 
> * Request based dm isn't converted yet.  dm_init_request_based_queue()
>   resets flush support to 0 for now.  To avoid disturbing request
>   based dm code, dm->flush_error is added for bio based dm while
>   requested based dm continues to use dm->barrier_error.
> 
> Lightly tested linear, stripe, raid1, snap and crypt targets.  Please
> proceed with caution as I'm not familiar with the code base.
> 
> Signed-off-by: Tejun Heo <tj kernel org>
> Cc: dm-devel redhat com
> Cc: Christoph Hellwig <hch lst de>
> ---
>  drivers/md/dm-crypt.c           |    2 +-
>  drivers/md/dm-io.c              |   20 +-----
>  drivers/md/dm-log.c             |    2 +-
>  drivers/md/dm-raid1.c           |    8 +-
>  drivers/md/dm-region-hash.c     |   16 +++---
>  drivers/md/dm-snap-persistent.c |    2 +-
>  drivers/md/dm-snap.c            |    6 +-
>  drivers/md/dm-stripe.c          |    2 +-
>  drivers/md/dm.c                 |  119 +++++++++++++++++++--------------------
>  9 files changed, 80 insertions(+), 97 deletions(-)
> 
> diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c
> index 368e8e9..d5b0e4c 100644
> --- a/drivers/md/dm-crypt.c
> +++ b/drivers/md/dm-crypt.c
> @@ -1278,7 +1278,7 @@ static int crypt_map(struct dm_target *ti, struct bio *bio,
>  	struct dm_crypt_io *io;
>  	struct crypt_config *cc;
>  
> -	if (unlikely(bio_empty_barrier(bio))) {
> +	if (bio->bi_rw & REQ_FLUSH) {
>  		cc = ti->private;
>  		bio->bi_bdev = cc->dev->bdev;
>  		return DM_MAPIO_REMAPPED;
> diff --git a/drivers/md/dm-io.c b/drivers/md/dm-io.c
> index 0590c75..136d4f7 100644
> --- a/drivers/md/dm-io.c
> +++ b/drivers/md/dm-io.c
> @@ -31,7 +31,6 @@ struct dm_io_client {
>   */
>  struct io {
>  	unsigned long error_bits;
> -	unsigned long eopnotsupp_bits;
>  	atomic_t count;
>  	struct task_struct *sleeper;
>  	struct dm_io_client *client;
> @@ -130,11 +129,8 @@ static void retrieve_io_and_region_from_bio(struct bio *bio, struct io **io,
>   *---------------------------------------------------------------*/
>  static void dec_count(struct io *io, unsigned int region, int error)
>  {
> -	if (error) {
> +	if (error)
>  		set_bit(region, &io->error_bits);
> -		if (error == -EOPNOTSUPP)
> -			set_bit(region, &io->eopnotsupp_bits);
> -	}
>  
>  	if (atomic_dec_and_test(&io->count)) {
>  		if (io->sleeper)
> @@ -310,8 +306,8 @@ static void do_region(int rw, unsigned region, struct dm_io_region *where,
>  	sector_t remaining = where->count;
>  
>  	/*
> -	 * where->count may be zero if rw holds a write barrier and we
> -	 * need to send a zero-sized barrier.
> +	 * where->count may be zero if rw holds a flush and we need to
> +	 * send a zero-sized flush.
>  	 */
>  	do {
>  		/*
> @@ -364,7 +360,7 @@ static void dispatch_io(int rw, unsigned int num_regions,
>  	 */
>  	for (i = 0; i < num_regions; i++) {
>  		*dp = old_pages;
> -		if (where[i].count || (rw & REQ_HARDBARRIER))
> +		if (where[i].count || (rw & REQ_FLUSH))
>  			do_region(rw, i, where + i, dp, io);
>  	}
>  
> @@ -393,9 +389,7 @@ static int sync_io(struct dm_io_client *client, unsigned int num_regions,
>  		return -EIO;
>  	}
>  
> -retry:
>  	io->error_bits = 0;
> -	io->eopnotsupp_bits = 0;
>  	atomic_set(&io->count, 1); /* see dispatch_io() */
>  	io->sleeper = current;
>  	io->client = client;
> @@ -412,11 +406,6 @@ retry:
>  	}
>  	set_current_state(TASK_RUNNING);
>  
> -	if (io->eopnotsupp_bits && (rw & REQ_HARDBARRIER)) {
> -		rw &= ~REQ_HARDBARRIER;
> -		goto retry;
> -	}
> -
>  	if (error_bits)
>  		*error_bits = io->error_bits;
>  
> @@ -437,7 +426,6 @@ static int async_io(struct dm_io_client *client, unsigned int num_regions,
>  
>  	io = mempool_alloc(client->pool, GFP_NOIO);
>  	io->error_bits = 0;
> -	io->eopnotsupp_bits = 0;
>  	atomic_set(&io->count, 1); /* see dispatch_io() */
>  	io->sleeper = NULL;
>  	io->client = client;
> diff --git a/drivers/md/dm-log.c b/drivers/md/dm-log.c
> index 5a08be0..33420e6 100644
> --- a/drivers/md/dm-log.c
> +++ b/drivers/md/dm-log.c
> @@ -300,7 +300,7 @@ static int flush_header(struct log_c *lc)
>  		.count = 0,
>  	};
>  
> -	lc->io_req.bi_rw = WRITE_BARRIER;
> +	lc->io_req.bi_rw = WRITE_FLUSH;
>  
>  	return dm_io(&lc->io_req, 1, &null_location, NULL);
>  }
> diff --git a/drivers/md/dm-raid1.c b/drivers/md/dm-raid1.c
> index 7c081bc..19a59b0 100644
> --- a/drivers/md/dm-raid1.c
> +++ b/drivers/md/dm-raid1.c
> @@ -259,7 +259,7 @@ static int mirror_flush(struct dm_target *ti)
>  	struct dm_io_region io[ms->nr_mirrors];
>  	struct mirror *m;
>  	struct dm_io_request io_req = {
> -		.bi_rw = WRITE_BARRIER,
> +		.bi_rw = WRITE_FLUSH,
>  		.mem.type = DM_IO_KMEM,
>  		.mem.ptr.bvec = NULL,
>  		.client = ms->io_client,
> @@ -629,7 +629,7 @@ static void do_write(struct mirror_set *ms, struct bio *bio)
>  	struct dm_io_region io[ms->nr_mirrors], *dest = io;
>  	struct mirror *m;
>  	struct dm_io_request io_req = {
> -		.bi_rw = WRITE | (bio->bi_rw & WRITE_BARRIER),
> +		.bi_rw = WRITE | (bio->bi_rw & WRITE_FLUSH_FUA),
>  		.mem.type = DM_IO_BVEC,
>  		.mem.ptr.bvec = bio->bi_io_vec + bio->bi_idx,
>  		.notify.fn = write_callback,
> @@ -670,7 +670,7 @@ static void do_writes(struct mirror_set *ms, struct bio_list *writes)
>  	bio_list_init(&requeue);
>  
>  	while ((bio = bio_list_pop(writes))) {
> -		if (unlikely(bio_empty_barrier(bio))) {
> +		if (bio->bi_rw & REQ_FLUSH) {
>  			bio_list_add(&sync, bio);
>  			continue;
>  		}
> @@ -1203,7 +1203,7 @@ static int mirror_end_io(struct dm_target *ti, struct bio *bio,
>  	 * We need to dec pending if this was a write.
>  	 */
>  	if (rw == WRITE) {
> -		if (likely(!bio_empty_barrier(bio)))
> +		if (!(bio->bi_rw & REQ_FLUSH))
>  			dm_rh_dec(ms->rh, map_context->ll);
>  		return error;
>  	}
> diff --git a/drivers/md/dm-region-hash.c b/drivers/md/dm-region-hash.c
> index bd5c58b..dad011a 100644
> --- a/drivers/md/dm-region-hash.c
> +++ b/drivers/md/dm-region-hash.c
> @@ -81,9 +81,9 @@ struct dm_region_hash {
>  	struct list_head failed_recovered_regions;
>  
>  	/*
> -	 * If there was a barrier failure no regions can be marked clean.
> +	 * If there was a flush failure no regions can be marked clean.
>  	 */
> -	int barrier_failure;
> +	int flush_failure;
>  
>  	void *context;
>  	sector_t target_begin;
> @@ -217,7 +217,7 @@ struct dm_region_hash *dm_region_hash_create(
>  	INIT_LIST_HEAD(&rh->quiesced_regions);
>  	INIT_LIST_HEAD(&rh->recovered_regions);
>  	INIT_LIST_HEAD(&rh->failed_recovered_regions);
> -	rh->barrier_failure = 0;
> +	rh->flush_failure = 0;
>  
>  	rh->region_pool = mempool_create_kmalloc_pool(MIN_REGIONS,
>  						      sizeof(struct dm_region));
> @@ -399,8 +399,8 @@ void dm_rh_mark_nosync(struct dm_region_hash *rh, struct bio *bio)
>  	region_t region = dm_rh_bio_to_region(rh, bio);
>  	int recovering = 0;
>  
> -	if (bio_empty_barrier(bio)) {
> -		rh->barrier_failure = 1;
> +	if (bio->bi_rw & REQ_FLUSH) {
> +		rh->flush_failure = 1;
>  		return;
>  	}
>  
> @@ -524,7 +524,7 @@ void dm_rh_inc_pending(struct dm_region_hash *rh, struct bio_list *bios)
>  	struct bio *bio;
>  
>  	for (bio = bios->head; bio; bio = bio->bi_next) {
> -		if (bio_empty_barrier(bio))
> +		if (bio->bi_rw & REQ_FLUSH)
>  			continue;
>  		rh_inc(rh, dm_rh_bio_to_region(rh, bio));
>  	}
> @@ -555,9 +555,9 @@ void dm_rh_dec(struct dm_region_hash *rh, region_t region)
>  		 */
>  
>  		/* do nothing for DM_RH_NOSYNC */
> -		if (unlikely(rh->barrier_failure)) {
> +		if (unlikely(rh->flush_failure)) {
>  			/*
> -			 * If a write barrier failed some time ago, we
> +			 * If a write flush failed some time ago, we
>  			 * don't know whether or not this write made it
>  			 * to the disk, so we must resync the device.
>  			 */
> diff --git a/drivers/md/dm-snap-persistent.c b/drivers/md/dm-snap-persistent.c
> index cc2bdb8..0b61792 100644
> --- a/drivers/md/dm-snap-persistent.c
> +++ b/drivers/md/dm-snap-persistent.c
> @@ -687,7 +687,7 @@ static void persistent_commit_exception(struct dm_exception_store *store,
>  	/*
>  	 * Commit exceptions to disk.
>  	 */
> -	if (ps->valid && area_io(ps, WRITE_BARRIER))
> +	if (ps->valid && area_io(ps, WRITE_FLUSH_FUA))
>  		ps->valid = 0;
>  
>  	/*
> diff --git a/drivers/md/dm-snap.c b/drivers/md/dm-snap.c
> index 5974d30..eed2101 100644
> --- a/drivers/md/dm-snap.c
> +++ b/drivers/md/dm-snap.c
> @@ -1587,7 +1587,7 @@ static int snapshot_map(struct dm_target *ti, struct bio *bio,
>  	chunk_t chunk;
>  	struct dm_snap_pending_exception *pe = NULL;
>  
> -	if (unlikely(bio_empty_barrier(bio))) {
> +	if (bio->bi_rw & REQ_FLUSH) {
>  		bio->bi_bdev = s->cow->bdev;
>  		return DM_MAPIO_REMAPPED;
>  	}
> @@ -1691,7 +1691,7 @@ static int snapshot_merge_map(struct dm_target *ti, struct bio *bio,
>  	int r = DM_MAPIO_REMAPPED;
>  	chunk_t chunk;
>  
> -	if (unlikely(bio_empty_barrier(bio))) {
> +	if (bio->bi_rw & REQ_FLUSH) {
>  		if (!map_context->target_request_nr)
>  			bio->bi_bdev = s->origin->bdev;
>  		else
> @@ -2135,7 +2135,7 @@ static int origin_map(struct dm_target *ti, struct bio *bio,
>  	struct dm_dev *dev = ti->private;
>  	bio->bi_bdev = dev->bdev;
>  
> -	if (unlikely(bio_empty_barrier(bio)))
> +	if (bio->bi_rw & REQ_FLUSH)
>  		return DM_MAPIO_REMAPPED;
>  
>  	/* Only tell snapshots if this is a write */
> diff --git a/drivers/md/dm-stripe.c b/drivers/md/dm-stripe.c
> index c297f6d..f0371b4 100644
> --- a/drivers/md/dm-stripe.c
> +++ b/drivers/md/dm-stripe.c
> @@ -271,7 +271,7 @@ static int stripe_map(struct dm_target *ti, struct bio *bio,
>  	uint32_t stripe;
>  	unsigned target_request_nr;
>  
> -	if (unlikely(bio_empty_barrier(bio))) {
> +	if (bio->bi_rw & REQ_FLUSH) {
>  		target_request_nr = map_context->target_request_nr;
>  		BUG_ON(target_request_nr >= sc->stripes);
>  		bio->bi_bdev = sc->stripe[target_request_nr].dev->bdev;
> diff --git a/drivers/md/dm.c b/drivers/md/dm.c
> index b1d92be..32e6622 100644
> --- a/drivers/md/dm.c
> +++ b/drivers/md/dm.c
> @@ -144,15 +144,16 @@ struct mapped_device {
>  	spinlock_t deferred_lock;
>  
>  	/*
> -	 * An error from the barrier request currently being processed.
> +	 * An error from the flush request currently being processed.
>  	 */
> -	int barrier_error;
> +	int flush_error;
>  
>  	/*
>  	 * Protect barrier_error from concurrent endio processing
>  	 * in request-based dm.
>  	 */
>  	spinlock_t barrier_error_lock;
> +	int barrier_error;
>  
>  	/*
>  	 * Processing queue (flush/barriers)
> @@ -200,8 +201,8 @@ struct mapped_device {
>  	/* sysfs handle */
>  	struct kobject kobj;
>  
> -	/* zero-length barrier that will be cloned and submitted to targets */
> -	struct bio barrier_bio;
> +	/* zero-length flush that will be cloned and submitted to targets */
> +	struct bio flush_bio;
>  };
>  
>  /*
> @@ -512,7 +513,7 @@ static void end_io_acct(struct dm_io *io)
>  
>  	/*
>  	 * After this is decremented the bio must not be touched if it is
> -	 * a barrier.
> +	 * a flush.
>  	 */
>  	dm_disk(md)->part0.in_flight[rw] = pending =
>  		atomic_dec_return(&md->pending[rw]);
> @@ -626,7 +627,7 @@ static void dec_pending(struct dm_io *io, int error)
>  			 */
>  			spin_lock_irqsave(&md->deferred_lock, flags);
>  			if (__noflush_suspending(md)) {
> -				if (!(io->bio->bi_rw & REQ_HARDBARRIER))
> +				if (!(io->bio->bi_rw & REQ_FLUSH))
>  					bio_list_add_head(&md->deferred,
>  							  io->bio);
>  			} else
> @@ -638,20 +639,14 @@ static void dec_pending(struct dm_io *io, int error)
>  		io_error = io->error;
>  		bio = io->bio;
>  
> -		if (bio->bi_rw & REQ_HARDBARRIER) {
> +		if (bio->bi_rw & REQ_FLUSH) {
>  			/*
> -			 * There can be just one barrier request so we use
> +			 * There can be just one flush request so we use
>  			 * a per-device variable for error reporting.
>  			 * Note that you can't touch the bio after end_io_acct
> -			 *
> -			 * We ignore -EOPNOTSUPP for empty flush reported by
> -			 * underlying devices. We assume that if the device
> -			 * doesn't support empty barriers, it doesn't need
> -			 * cache flushing commands.
>  			 */
> -			if (!md->barrier_error &&
> -			    !(bio_empty_barrier(bio) && io_error == -EOPNOTSUPP))
> -				md->barrier_error = io_error;
> +			if (!md->flush_error)
> +				md->flush_error = io_error;
>  			end_io_acct(io);
>  			free_io(md, io);
>  		} else {
> @@ -1119,7 +1114,7 @@ static void dm_bio_destructor(struct bio *bio)
>  }
>  
>  /*
> - * Creates a little bio that is just does part of a bvec.
> + * Creates a little bio that just does part of a bvec.
>   */
>  static struct bio *split_bvec(struct bio *bio, sector_t sector,
>  			      unsigned short idx, unsigned int offset,
> @@ -1134,7 +1129,7 @@ static struct bio *split_bvec(struct bio *bio, sector_t sector,
>  
>  	clone->bi_sector = sector;
>  	clone->bi_bdev = bio->bi_bdev;
> -	clone->bi_rw = bio->bi_rw & ~REQ_HARDBARRIER;
> +	clone->bi_rw = bio->bi_rw;
>  	clone->bi_vcnt = 1;
>  	clone->bi_size = to_bytes(len);
>  	clone->bi_io_vec->bv_offset = offset;
> @@ -1161,7 +1156,6 @@ static struct bio *clone_bio(struct bio *bio, sector_t sector,
>  
>  	clone = bio_alloc_bioset(GFP_NOIO, bio->bi_max_vecs, bs);
>  	__bio_clone(clone, bio);
> -	clone->bi_rw &= ~REQ_HARDBARRIER;
>  	clone->bi_destructor = dm_bio_destructor;
>  	clone->bi_sector = sector;
>  	clone->bi_idx = idx;
> @@ -1225,7 +1219,7 @@ static void __issue_target_requests(struct clone_info *ci, struct dm_target *ti,
>  		__issue_target_request(ci, ti, request_nr, len);
>  }
>  
> -static int __clone_and_map_empty_barrier(struct clone_info *ci)
> +static int __clone_and_map_flush(struct clone_info *ci)
>  {
>  	unsigned target_nr = 0;
>  	struct dm_target *ti;
> @@ -1289,9 +1283,6 @@ static int __clone_and_map(struct clone_info *ci)
>  	sector_t len = 0, max;
>  	struct dm_target_io *tio;
>  
> -	if (unlikely(bio_empty_barrier(bio)))
> -		return __clone_and_map_empty_barrier(ci);
> -
>  	if (unlikely(bio->bi_rw & REQ_DISCARD))
>  		return __clone_and_map_discard(ci);
>  
> @@ -1383,11 +1374,11 @@ static void __split_and_process_bio(struct mapped_device *md, struct bio *bio)
>  
>  	ci.map = dm_get_live_table(md);
>  	if (unlikely(!ci.map)) {
> -		if (!(bio->bi_rw & REQ_HARDBARRIER))
> +		if (!(bio->bi_rw & REQ_FLUSH))
>  			bio_io_error(bio);
>  		else
> -			if (!md->barrier_error)
> -				md->barrier_error = -EIO;
> +			if (!md->flush_error)
> +				md->flush_error = -EIO;
>  		return;
>  	}
>  
> @@ -1400,14 +1391,22 @@ static void __split_and_process_bio(struct mapped_device *md, struct bio *bio)
>  	ci.io->md = md;
>  	spin_lock_init(&ci.io->endio_lock);
>  	ci.sector = bio->bi_sector;
> -	ci.sector_count = bio_sectors(bio);
> -	if (unlikely(bio_empty_barrier(bio)))
> +	if (!(bio->bi_rw & REQ_FLUSH))
> +		ci.sector_count = bio_sectors(bio);
> +	else {
> +		/* all FLUSH bio's reaching here should be empty */
> +		WARN_ON_ONCE(bio_has_data(bio));
>  		ci.sector_count = 1;
> +	}
>  	ci.idx = bio->bi_idx;
>  
>  	start_io_acct(ci.io);
> -	while (ci.sector_count && !error)
> -		error = __clone_and_map(&ci);
> +	while (ci.sector_count && !error) {
> +		if (!(bio->bi_rw & REQ_FLUSH))
> +			error = __clone_and_map(&ci);
> +		else
> +			error = __clone_and_map_flush(&ci);
> +	}
>  
>  	/* drop the extra reference count */
>  	dec_pending(ci.io, error);
> @@ -1492,11 +1491,11 @@ static int _dm_request(struct request_queue *q, struct bio *bio)
>  	part_stat_unlock();
>  
>  	/*
> -	 * If we're suspended or the thread is processing barriers
> +	 * If we're suspended or the thread is processing flushes
>  	 * we have to queue this io for later.
>  	 */
>  	if (unlikely(test_bit(DMF_QUEUE_IO_TO_THREAD, &md->flags)) ||
> -	    unlikely(bio->bi_rw & REQ_HARDBARRIER)) {
> +	    (bio->bi_rw & REQ_FLUSH)) {
>  		up_read(&md->io_lock);
>  
>  		if (unlikely(test_bit(DMF_BLOCK_IO_FOR_SUSPEND, &md->flags)) &&
> @@ -1940,6 +1939,7 @@ static void dm_init_md_queue(struct mapped_device *md)
>  	blk_queue_bounce_limit(md->queue, BLK_BOUNCE_ANY);
>  	md->queue->unplug_fn = dm_unplug_all;
>  	blk_queue_merge_bvec(md->queue, dm_merge_bvec);
> +	blk_queue_flush(md->queue, REQ_FLUSH | REQ_FUA);
>  }
>  
>  /*
> @@ -2245,7 +2245,8 @@ static int dm_init_request_based_queue(struct mapped_device *md)
>  	blk_queue_softirq_done(md->queue, dm_softirq_done);
>  	blk_queue_prep_rq(md->queue, dm_prep_fn);
>  	blk_queue_lld_busy(md->queue, dm_lld_busy);
> -	blk_queue_flush(md->queue, REQ_FLUSH);
> +	/* no flush support for request based dm yet */
> +	blk_queue_flush(md->queue, 0);
>  
>  	elv_register_queue(md->queue);
>  
> @@ -2406,41 +2407,35 @@ static int dm_wait_for_completion(struct mapped_device *md, int interruptible)
>  	return r;
>  }
>  
> -static void dm_flush(struct mapped_device *md)
> +static void process_flush(struct mapped_device *md, struct bio *bio)
>  {
> -	dm_wait_for_completion(md, TASK_UNINTERRUPTIBLE);
> -
> -	bio_init(&md->barrier_bio);
> -	md->barrier_bio.bi_bdev = md->bdev;
> -	md->barrier_bio.bi_rw = WRITE_BARRIER;
> -	__split_and_process_bio(md, &md->barrier_bio);
> +	md->flush_error = 0;
>  
> +	/* handle REQ_FLUSH */
>  	dm_wait_for_completion(md, TASK_UNINTERRUPTIBLE);
> -}
>  
> -static void process_barrier(struct mapped_device *md, struct bio *bio)
> -{
> -	md->barrier_error = 0;
> +	bio_init(&md->flush_bio);
> +	md->flush_bio.bi_bdev = md->bdev;
> +	md->flush_bio.bi_rw = WRITE_FLUSH;
> +	__split_and_process_bio(md, &md->flush_bio);
>  
> -	dm_flush(md);
> +	dm_wait_for_completion(md, TASK_UNINTERRUPTIBLE);
>  
> -	if (!bio_empty_barrier(bio)) {
> -		__split_and_process_bio(md, bio);
> -		/*
> -		 * If the request isn't supported, don't waste time with
> -		 * the second flush.
> -		 */
> -		if (md->barrier_error != -EOPNOTSUPP)
> -			dm_flush(md);
> +	/* if it's an empty flush or the preflush failed, we're done */
> +	if (!bio_has_data(bio) || md->flush_error) {
> +		if (md->flush_error != DM_ENDIO_REQUEUE)
> +			bio_endio(bio, md->flush_error);
> +		else {
> +			spin_lock_irq(&md->deferred_lock);
> +			bio_list_add_head(&md->deferred, bio);
> +			spin_unlock_irq(&md->deferred_lock);
> +		}
> +		return;
>  	}
>  
> -	if (md->barrier_error != DM_ENDIO_REQUEUE)
> -		bio_endio(bio, md->barrier_error);
> -	else {
> -		spin_lock_irq(&md->deferred_lock);
> -		bio_list_add_head(&md->deferred, bio);
> -		spin_unlock_irq(&md->deferred_lock);
> -	}
> +	/* issue data + REQ_FUA */
> +	bio->bi_rw &= ~REQ_FLUSH;
> +	__split_and_process_bio(md, bio);
>  }
>  
>  /*
> @@ -2469,8 +2464,8 @@ static void dm_wq_work(struct work_struct *work)
>  		if (dm_request_based(md))
>  			generic_make_request(c);
>  		else {
> -			if (c->bi_rw & REQ_HARDBARRIER)
> -				process_barrier(md, c);
> +			if (c->bi_rw & REQ_FLUSH)
> +				process_flush(md, c);
>  			else
>  				__split_and_process_bio(md, c);
>  		}
> -- 
> 1.7.1
> 


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