md/raid10: simplify the splitting of requests.

raid10 splits requests in two different ways for two different
reasons.

First, bio_split() is used to ensure the bio fits with a chunk.
Second, multiple r10bio structures are allocated to represent the
different sections that need to go to different devices, to avoid
known bad blocks.

This can be simplified to just use bio_split() once, and not to use
multiple r10bios.
We delay the split until we know a maximum bio size that can
be handled with a single r10bio, and then split the bio and queue
the remainder for later handling.

As with raid1, we allocate a new bio_set to help with the splitting.
It is not correct to use fs_bio_set in a device driver.

Signed-off-by: NeilBrown <neilb@suse.com>
Signed-off-by: Shaohua Li <shli@fb.com>

2 files changed, 51 insertions, 114 deletions

diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index e055ec94b9a8..41845bae67be 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -1127,7 +1127,6 @@ static void raid10_read_request(struct mddev *mddev, struct bio *bio,
         struct bio *read_bio;
         const int op = bio_op(bio);
         const unsigned long do_sync = (bio->bi_opf & REQ_SYNC);
-        int sectors_handled;
         int max_sectors;
         sector_t sectors;
         struct md_rdev *rdev;
@@ -1140,7 +1139,7 @@ static void raid10_read_request(struct mddev *mddev, struct bio *bio,
          */
         wait_barrier(conf);
 
-        sectors = bio_sectors(bio);
+        sectors = r10_bio->sectors;
         while (test_bit(MD_RECOVERY_RESHAPE, &mddev->recovery) &&
             bio->bi_iter.bi_sector < conf->reshape_progress &&
             bio->bi_iter.bi_sector + sectors > conf->reshape_progress) {
@@ -1157,17 +1156,23 @@ static void raid10_read_request(struct mddev *mddev, struct bio *bio,
                 wait_barrier(conf);
         }
 
-read_again:
         rdev = read_balance(conf, r10_bio, &max_sectors);
         if (!rdev) {
                 raid_end_bio_io(r10_bio);
                 return;
         }
+        if (max_sectors < bio_sectors(bio)) {
+                struct bio *split = bio_split(bio, max_sectors,
+                                              GFP_NOIO, conf->bio_split);
+                bio_chain(split, bio);
+                generic_make_request(bio);
+                bio = split;
+                r10_bio->master_bio = bio;
+                r10_bio->sectors = max_sectors;
+        }
         slot = r10_bio->read_slot;
 
         read_bio = bio_clone_fast(bio, GFP_NOIO, mddev->bio_set);
-        bio_trim(read_bio, r10_bio->sector - bio->bi_iter.bi_sector,
-                 max_sectors);
 
         r10_bio->devs[slot].bio = read_bio;
         r10_bio->devs[slot].rdev = rdev;
@@ -1186,40 +1191,13 @@ read_again:
                 trace_block_bio_remap(bdev_get_queue(read_bio->bi_bdev),
                                       read_bio, disk_devt(mddev->gendisk),
                                       r10_bio->sector);
-        if (max_sectors < r10_bio->sectors) {
-                /*
-                 * Could not read all from this device, so we will need another
-                 * r10_bio.
-                 */
-                sectors_handled = (r10_bio->sector + max_sectors
-                                   - bio->bi_iter.bi_sector);
-                r10_bio->sectors = max_sectors;
-                inc_pending(conf);
-                bio_inc_remaining(bio);
-                /*
-                 * Cannot call generic_make_request directly as that will be
-                 * queued in __generic_make_request and subsequent
-                 * mempool_alloc might block waiting for it.  so hand bio over
-                 * to raid10d.
-                 */
-                reschedule_retry(r10_bio);
-
-                r10_bio = mempool_alloc(conf->r10bio_pool, GFP_NOIO);
-
-                r10_bio->master_bio = bio;
-                r10_bio->sectors = bio_sectors(bio) - sectors_handled;
-                r10_bio->state = 0;
-                r10_bio->mddev = mddev;
-                r10_bio->sector = bio->bi_iter.bi_sector + sectors_handled;
-                goto read_again;
-        } else
-                generic_make_request(read_bio);
+        generic_make_request(read_bio);
         return;
 }
 
 static void raid10_write_one_disk(struct mddev *mddev, struct r10bio *r10_bio,
                                   struct bio *bio, bool replacement,
-                                  int n_copy, int max_sectors)
+                                  int n_copy)
 {
         const int op = bio_op(bio);
         const unsigned long do_sync = (bio->bi_opf & REQ_SYNC);
@@ -1243,7 +1221,6 @@ static void raid10_write_one_disk(struct mddev *mddev, struct r10bio *r10_bio,
                 rdev = conf->mirrors[devnum].rdev;
 
         mbio = bio_clone_fast(bio, GFP_NOIO, mddev->bio_set);
-        bio_trim(mbio, r10_bio->sector - bio->bi_iter.bi_sector, max_sectors);
         if (replacement)
                 r10_bio->devs[n_copy].repl_bio = mbio;
         else
@@ -1294,7 +1271,6 @@ static void raid10_write_request(struct mddev *mddev, struct bio *bio,
         int i;
         struct md_rdev *blocked_rdev;
         sector_t sectors;
-        int sectors_handled;
         int max_sectors;
 
         md_write_start(mddev, bio);
@@ -1306,7 +1282,7 @@ static void raid10_write_request(struct mddev *mddev, struct bio *bio,
          */
         wait_barrier(conf);
 
-        sectors = bio_sectors(bio);
+        sectors = r10_bio->sectors;
         while (test_bit(MD_RECOVERY_RESHAPE, &mddev->recovery) &&
             bio->bi_iter.bi_sector < conf->reshape_progress &&
             bio->bi_iter.bi_sector + sectors > conf->reshape_progress) {
@@ -1476,44 +1452,29 @@ retry_write:
 
         if (max_sectors < r10_bio->sectors)
                 r10_bio->sectors = max_sectors;
-        sectors_handled = r10_bio->sector + max_sectors -
-                bio->bi_iter.bi_sector;
+
+        if (r10_bio->sectors < bio_sectors(bio)) {
+                struct bio *split = bio_split(bio, r10_bio->sectors,
+                                              GFP_NOIO, conf->bio_split);
+                bio_chain(split, bio);
+                generic_make_request(bio);
+                bio = split;
+                r10_bio->master_bio = bio;
+        }
 
         atomic_set(&r10_bio->remaining, 1);
         bitmap_startwrite(mddev->bitmap, r10_bio->sector, r10_bio->sectors, 0);
 
         for (i = 0; i < conf->copies; i++) {
                 if (r10_bio->devs[i].bio)
-                        raid10_write_one_disk(mddev, r10_bio, bio, false,
-                                              i, max_sectors);
+                        raid10_write_one_disk(mddev, r10_bio, bio, false, i);
                 if (r10_bio->devs[i].repl_bio)
-                        raid10_write_one_disk(mddev, r10_bio, bio, true,
-                                              i, max_sectors);
-        }
-
-        /* Don't remove the bias on 'remaining' (one_write_done) until
-         * after checking if we need to go around again.
-         */
-
-        if (sectors_handled < bio_sectors(bio)) {
-                /* We need another r10_bio and it needs to be counted */
-                inc_pending(conf);
-                bio_inc_remaining(bio);
-                one_write_done(r10_bio);
-                r10_bio = mempool_alloc(conf->r10bio_pool, GFP_NOIO);
-
-                r10_bio->master_bio = bio;
-                r10_bio->sectors = bio_sectors(bio) - sectors_handled;
-
-                r10_bio->mddev = mddev;
-                r10_bio->sector = bio->bi_iter.bi_sector + sectors_handled;
-                r10_bio->state = 0;
-                goto retry_write;
+                        raid10_write_one_disk(mddev, r10_bio, bio, true, i);
         }
         one_write_done(r10_bio);
 }
 
-static void __make_request(struct mddev *mddev, struct bio *bio)
+static void __make_request(struct mddev *mddev, struct bio *bio, int sectors)
 {
         struct r10conf *conf = mddev->private;
         struct r10bio *r10_bio;
@@ -1521,7 +1482,7 @@ static void __make_request(struct mddev *mddev, struct bio *bio)
         r10_bio = mempool_alloc(conf->r10bio_pool, GFP_NOIO);
 
         r10_bio->master_bio = bio;
-        r10_bio->sectors = bio_sectors(bio);
+        r10_bio->sectors = sectors;
 
         r10_bio->mddev = mddev;
         r10_bio->sector = bio->bi_iter.bi_sector;
@@ -1538,54 +1499,26 @@ static void raid10_make_request(struct mddev *mddev, struct bio *bio)
         struct r10conf *conf = mddev->private;
         sector_t chunk_mask = (conf->geo.chunk_mask & conf->prev.chunk_mask);
         int chunk_sects = chunk_mask + 1;
-
-        struct bio *split;
+        int sectors = bio_sectors(bio);
 
         if (unlikely(bio->bi_opf & REQ_PREFLUSH)) {
                 md_flush_request(mddev, bio);
                 return;
         }
 
-        do {
-
-                /*
-                 * If this request crosses a chunk boundary, we need to split
-                 * it.
-                 */
-                if (unlikely((bio->bi_iter.bi_sector & chunk_mask) +
-                             bio_sectors(bio) > chunk_sects
-                             && (conf->geo.near_copies < conf->geo.raid_disks
-                                 || conf->prev.near_copies <
-                                 conf->prev.raid_disks))) {
-                        split = bio_split(bio, chunk_sects -
-                                          (bio->bi_iter.bi_sector &
-                                           (chunk_sects - 1)),
-                                          GFP_NOIO, fs_bio_set);
-                        bio_chain(split, bio);
-                } else {
-                        split = bio;
-                }
-
-                /*
-                 * If a bio is splitted, the first part of bio will pass
-                 * barrier but the bio is queued in current->bio_list (see
-                 * generic_make_request). If there is a raise_barrier() called
-                 * here, the second part of bio can't pass barrier. But since
-                 * the first part bio isn't dispatched to underlaying disks
-                 * yet, the barrier is never released, hence raise_barrier will
-                 * alays wait. We have a deadlock.
-                 * Note, this only happens in read path. For write path, the
-                 * first part of bio is dispatched in a schedule() call
-                 * (because of blk plug) or offloaded to raid10d.
-                 * Quitting from the function immediately can change the bio
-                 * order queued in bio_list and avoid the deadlock.
-                 */
-                __make_request(mddev, split);
-                if (split != bio && bio_data_dir(bio) == READ) {
-                        generic_make_request(bio);
-                        break;
-                }
-        } while (split != bio);
+        /*
+         * If this request crosses a chunk boundary, we need to split
+         * it.
+         */
+        if (unlikely((bio->bi_iter.bi_sector & chunk_mask) +
+                     sectors > chunk_sects
+                     && (conf->geo.near_copies < conf->geo.raid_disks
+                         || conf->prev.near_copies <
+                         conf->prev.raid_disks)))
+                sectors = chunk_sects -
+                        (bio->bi_iter.bi_sector &
+                         (chunk_sects - 1));
+        __make_request(mddev, bio, sectors);
 
         /* In case raid10d snuck in to freeze_array */
         wake_up(&conf->wait_barrier);
@@ -2873,13 +2806,8 @@ static void raid10d(struct md_thread *thread)
                         recovery_request_write(mddev, r10_bio);
                 else if (test_bit(R10BIO_ReadError, &r10_bio->state))
                         handle_read_error(mddev, r10_bio);
-                else {
-                        /* just a partial read to be scheduled from a
-                         * separate context
-                         */
-                        int slot = r10_bio->read_slot;
-                        generic_make_request(r10_bio->devs[slot].bio);
-                }
+                else
+                        WARN_ON_ONCE(1);
 
                 cond_resched();
                 if (mddev->sb_flags & ~(1<<MD_SB_CHANGE_PENDING))
@@ -3652,6 +3580,10 @@ static struct r10conf *setup_conf(struct mddev *mddev)
         if (!conf->r10bio_pool)
                 goto out;
 
+        conf->bio_split = bioset_create(BIO_POOL_SIZE, 0);
+        if (!conf->bio_split)
+                goto out;
+
         calc_sectors(conf, mddev->dev_sectors);
         if (mddev->reshape_position == MaxSector) {
                 conf->prev = conf->geo;
@@ -3689,6 +3621,8 @@ static struct r10conf *setup_conf(struct mddev *mddev)
                 mempool_destroy(conf->r10bio_pool);
                 kfree(conf->mirrors);
                 safe_put_page(conf->tmppage);
+                if (conf->bio_split)
+                        bioset_free(conf->bio_split);
                 kfree(conf);
         }
         return ERR_PTR(err);
@@ -3899,6 +3833,8 @@ static void raid10_free(struct mddev *mddev, void *priv)
         kfree(conf->mirrors);
         kfree(conf->mirrors_old);
         kfree(conf->mirrors_new);
+        if (conf->bio_split)
+                bioset_free(conf->bio_split);
         kfree(conf);
 }
 
diff --git a/drivers/md/raid10.h b/drivers/md/raid10.h
index 3162615e57bd..735ce1a3d260 100644
--- a/drivers/md/raid10.h
+++ b/drivers/md/raid10.h
@@ -82,6 +82,7 @@ struct r10conf {
         mempool_t               *r10bio_pool;
         mempool_t               *r10buf_pool;
         struct page             *tmppage;
+        struct bio_set          *bio_split;
 
         /* When taking over an array from a different personality, we store
          * the new thread here until we fully activate the array.