dm: implement REQ_FLUSH/FUA support for bio-based dm

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>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

9 files changed, 80 insertions, 97 deletions

diff --git a/drivers/md/dm-crypt.c b/drivers/md/dm-crypt.c
index 368e8e98f705..d5b0e4c0e702 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 0590c75b0ab6..136d4f71a116 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 5a08be0222db..33420e68d153 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 7c081bcbc3cf..19a59b041c27 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 bd5c58b28868..dad011aed0c9 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 cc2bdb83f9ad..0b61792a2780 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 5974d3094d97..eed210152b75 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 c297f6da91ea..f0371b4c4fbf 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 b1d92be8f990..32e6622767ad 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);
                 }