dm cache: simplify deferred set reference count increments

Factor out inc_and_issue and inc_ds helpers to simplify deferred set
reference count increments.  Also cleanup cache_map to consistently call
cell_defer and inc_ds when the bio is DM_MAPIO_REMAPPED.

No functional change.

Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

1 files changed, 77 insertions, 46 deletions

diff --git a/drivers/md/dm-cache-target.c b/drivers/md/dm-cache-target.c
index 2c63326638b6..2a156af246b2 100644
--- a/drivers/md/dm-cache-target.c
+++ b/drivers/md/dm-cache-target.c
@@ -718,6 +718,22 @@ static int bio_triggers_commit(struct cache *cache, struct bio *bio)
         return bio->bi_rw & (REQ_FLUSH | REQ_FUA);
 }
 
+/*
+ * You must increment the deferred set whilst the prison cell is held.  To
+ * encourage this, we ask for 'cell' to be passed in.
+ */
+static void inc_ds(struct cache *cache, struct bio *bio,
+                   struct dm_bio_prison_cell *cell)
+{
+        size_t pb_data_size = get_per_bio_data_size(cache);
+        struct per_bio_data *pb = get_per_bio_data(bio, pb_data_size);
+
+        BUG_ON(!cell);
+        BUG_ON(pb->all_io_entry);
+
+        pb->all_io_entry = dm_deferred_entry_inc(cache->all_io_ds);
+}
+
 static void issue(struct cache *cache, struct bio *bio)
 {
         unsigned long flags;
@@ -737,6 +753,12 @@ static void issue(struct cache *cache, struct bio *bio)
         spin_unlock_irqrestore(&cache->lock, flags);
 }
 
+static void inc_and_issue(struct cache *cache, struct bio *bio, struct dm_bio_prison_cell *cell)
+{
+        inc_ds(cache, bio, cell);
+        issue(cache, bio);
+}
+
 static void defer_writethrough_bio(struct cache *cache, struct bio *bio)
 {
         unsigned long flags;
@@ -1015,6 +1037,11 @@ static void issue_overwrite(struct dm_cache_migration *mg, struct bio *bio)
 
         dm_hook_bio(&pb->hook_info, bio, overwrite_endio, mg);
         remap_to_cache_dirty(mg->cache, bio, mg->new_oblock, mg->cblock);
+
+        /*
+         * No need to inc_ds() here, since the cell will be held for the
+         * duration of the io.
+         */
         generic_make_request(bio);
 }
 
@@ -1115,8 +1142,7 @@ static void check_for_quiesced_migrations(struct cache *cache,
                 return;
 
         INIT_LIST_HEAD(&work);
-        if (pb->all_io_entry)
-                dm_deferred_entry_dec(pb->all_io_entry, &work);
+        dm_deferred_entry_dec(pb->all_io_entry, &work);
 
         if (!list_empty(&work))
                 queue_quiesced_migrations(cache, &work);
@@ -1252,6 +1278,11 @@ static void process_flush_bio(struct cache *cache, struct bio *bio)
         else
                 remap_to_cache(cache, bio, 0);
 
+        /*
+         * REQ_FLUSH is not directed at any particular block so we don't
+         * need to inc_ds().  REQ_FUA's are split into a write + REQ_FLUSH
+         * by dm-core.
+         */
         issue(cache, bio);
 }
 
@@ -1301,15 +1332,6 @@ static void inc_miss_counter(struct cache *cache, struct bio *bio)
                    &cache->stats.read_miss : &cache->stats.write_miss);
 }
 
-static void issue_cache_bio(struct cache *cache, struct bio *bio,
-                            struct per_bio_data *pb,
-                            dm_oblock_t oblock, dm_cblock_t cblock)
-{
-        pb->all_io_entry = dm_deferred_entry_inc(cache->all_io_ds);
-        remap_to_cache_dirty(cache, bio, oblock, cblock);
-        issue(cache, bio);
-}
-
 static void process_bio(struct cache *cache, struct prealloc *structs,
                         struct bio *bio)
 {
@@ -1318,8 +1340,6 @@ static void process_bio(struct cache *cache, struct prealloc *structs,
         dm_oblock_t block = get_bio_block(cache, bio);
         struct dm_bio_prison_cell *cell_prealloc, *old_ocell, *new_ocell;
         struct policy_result lookup_result;
-        size_t pb_data_size = get_per_bio_data_size(cache);
-        struct per_bio_data *pb = get_per_bio_data(bio, pb_data_size);
         bool discarded_block = is_discarded_oblock(cache, block);
         bool passthrough = passthrough_mode(&cache->features);
         bool can_migrate = !passthrough && (discarded_block || spare_migration_bandwidth(cache));
@@ -1359,9 +1379,8 @@ static void process_bio(struct cache *cache, struct prealloc *structs,
 
                         } else {
                                 /* FIXME: factor out issue_origin() */
-                                pb->all_io_entry = dm_deferred_entry_inc(cache->all_io_ds);
                                 remap_to_origin_clear_discard(cache, bio, block);
-                                issue(cache, bio);
+                                inc_and_issue(cache, bio, new_ocell);
                         }
                 } else {
                         inc_hit_counter(cache, bio);
@@ -1369,20 +1388,21 @@ static void process_bio(struct cache *cache, struct prealloc *structs,
                         if (bio_data_dir(bio) == WRITE &&
                             writethrough_mode(&cache->features) &&
                             !is_dirty(cache, lookup_result.cblock)) {
-                                pb->all_io_entry = dm_deferred_entry_inc(cache->all_io_ds);
                                 remap_to_origin_then_cache(cache, bio, block, lookup_result.cblock);
-                                issue(cache, bio);
-                        } else
-                                issue_cache_bio(cache, bio, pb, block, lookup_result.cblock);
+                                inc_and_issue(cache, bio, new_ocell);
+
+                        } else  {
+                                remap_to_cache_dirty(cache, bio, block, lookup_result.cblock);
+                                inc_and_issue(cache, bio, new_ocell);
+                        }
                 }
 
                 break;
 
         case POLICY_MISS:
                 inc_miss_counter(cache, bio);
-                pb->all_io_entry = dm_deferred_entry_inc(cache->all_io_ds);
                 remap_to_origin_clear_discard(cache, bio, block);
-                issue(cache, bio);
+                inc_and_issue(cache, bio, new_ocell);
                 break;
 
         case POLICY_NEW:
@@ -1501,6 +1521,9 @@ static void process_deferred_flush_bios(struct cache *cache, bool submit_bios)
         bio_list_init(&cache->deferred_flush_bios);
         spin_unlock_irqrestore(&cache->lock, flags);
 
+        /*
+         * These bios have already been through inc_ds()
+         */
         while ((bio = bio_list_pop(&bios)))
                 submit_bios ? generic_make_request(bio) : bio_io_error(bio);
 }
@@ -1518,6 +1541,9 @@ static void process_deferred_writethrough_bios(struct cache *cache)
         bio_list_init(&cache->deferred_writethrough_bios);
         spin_unlock_irqrestore(&cache->lock, flags);
 
+        /*
+         * These bios have already been through inc_ds()
+         */
         while ((bio = bio_list_pop(&bios)))
                 generic_make_request(bio);
 }
@@ -2406,16 +2432,13 @@ out:
         return r;
 }
 
-static int cache_map(struct dm_target *ti, struct bio *bio)
+static int __cache_map(struct cache *cache, struct bio *bio, struct dm_bio_prison_cell **cell)
 {
-        struct cache *cache = ti->private;
-
         int r;
         dm_oblock_t block = get_bio_block(cache, bio);
         size_t pb_data_size = get_per_bio_data_size(cache);
         bool can_migrate = false;
         bool discarded_block;
-        struct dm_bio_prison_cell *cell;
         struct policy_result lookup_result;
         struct per_bio_data *pb = init_per_bio_data(bio, pb_data_size);
 
@@ -2437,15 +2460,15 @@ static int cache_map(struct dm_target *ti, struct bio *bio)
         /*
          * Check to see if that block is currently migrating.
          */
-        cell = alloc_prison_cell(cache);
-        if (!cell) {
+        *cell = alloc_prison_cell(cache);
+        if (!*cell) {
                 defer_bio(cache, bio);
                 return DM_MAPIO_SUBMITTED;
         }
 
-        r = bio_detain(cache, block, bio, cell,
+        r = bio_detain(cache, block, bio, *cell,
                        (cell_free_fn) free_prison_cell,
-                       cache, &cell);
+                       cache, cell);
         if (r) {
                 if (r < 0)
                         defer_bio(cache, bio);
@@ -2458,11 +2481,12 @@ static int cache_map(struct dm_target *ti, struct bio *bio)
         r = policy_map(cache->policy, block, false, can_migrate, discarded_block,
                        bio, &lookup_result);
         if (r == -EWOULDBLOCK) {
-                cell_defer(cache, cell, true);
+                cell_defer(cache, *cell, true);
                 return DM_MAPIO_SUBMITTED;
 
         } else if (r) {
                 DMERR_LIMIT("Unexpected return from cache replacement policy: %d", r);
+                cell_defer(cache, *cell, false);
                 bio_io_error(bio);
                 return DM_MAPIO_SUBMITTED;
         }
@@ -2476,52 +2500,44 @@ static int cache_map(struct dm_target *ti, struct bio *bio)
                                  * We need to invalidate this block, so
                                  * defer for the worker thread.
                                  */
-                                cell_defer(cache, cell, true);
+                                cell_defer(cache, *cell, true);
                                 r = DM_MAPIO_SUBMITTED;
 
                         } else {
-                                pb->all_io_entry = dm_deferred_entry_inc(cache->all_io_ds);
                                 inc_miss_counter(cache, bio);
                                 remap_to_origin_clear_discard(cache, bio, block);
-
-                                cell_defer(cache, cell, false);
                         }
 
                 } else {
                         inc_hit_counter(cache, bio);
-                        pb->all_io_entry = dm_deferred_entry_inc(cache->all_io_ds);
-
                         if (bio_data_dir(bio) == WRITE && writethrough_mode(&cache->features) &&
                             !is_dirty(cache, lookup_result.cblock))
                                 remap_to_origin_then_cache(cache, bio, block, lookup_result.cblock);
                         else
                                 remap_to_cache_dirty(cache, bio, block, lookup_result.cblock);
-
-                        cell_defer(cache, cell, false);
                 }
                 break;
 
         case POLICY_MISS:
                 inc_miss_counter(cache, bio);
-                pb->all_io_entry = dm_deferred_entry_inc(cache->all_io_ds);
-
                 if (pb->req_nr != 0) {
                         /*
                          * This is a duplicate writethrough io that is no
                          * longer needed because the block has been demoted.
                          */
                         bio_endio(bio, 0);
-                        cell_defer(cache, cell, false);
-                        return DM_MAPIO_SUBMITTED;
-                } else {
+                        cell_defer(cache, *cell, false);
+                        r = DM_MAPIO_SUBMITTED;
+
+                } else
                         remap_to_origin_clear_discard(cache, bio, block);
-                        cell_defer(cache, cell, false);
-                }
+
                 break;
 
         default:
                 DMERR_LIMIT("%s: erroring bio: unknown policy op: %u", __func__,
                             (unsigned) lookup_result.op);
+                cell_defer(cache, *cell, false);
                 bio_io_error(bio);
                 r = DM_MAPIO_SUBMITTED;
         }
@@ -2529,6 +2545,21 @@ static int cache_map(struct dm_target *ti, struct bio *bio)
         return r;
 }
 
+static int cache_map(struct dm_target *ti, struct bio *bio)
+{
+        int r;
+        struct dm_bio_prison_cell *cell;
+        struct cache *cache = ti->private;
+
+        r = __cache_map(cache, bio, &cell);
+        if (r == DM_MAPIO_REMAPPED) {
+                inc_ds(cache, bio, cell);
+                cell_defer(cache, cell, false);
+        }
+
+        return r;
+}
+
 static int cache_end_io(struct dm_target *ti, struct bio *bio, int error)
 {
         struct cache *cache = ti->private;
@@ -3072,7 +3103,7 @@ static void cache_io_hints(struct dm_target *ti, struct queue_limits *limits)
 
 static struct target_type cache_target = {
         .name = "cache",
-        .version = {1, 4, 0},
+        .version = {1, 5, 0},
         .module = THIS_MODULE,
         .ctr = cache_ctr,
         .dtr = cache_dtr,