3 stable fixes and 1 fix for a regression introduced during 3.19 merge:

- Fix inability to discard used space when the thin-pool target is in
   out-of-data-space mode and also transition the thin-pool back to write
   mode once free space is made available.
 
 - Fix DM core bio-based end_io bug that prevented proper post-processing
   of the error code returned from the block layer.
 
 - Fix crash in DM thin-pool due to thin device being added to the pool's
   active_thins list before properly initializing the thin device's
   refcount.
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Merge tag 'dm-3.19-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm

Pull device mapper fixes from Mike Snitzer:
 "Thre stable fixes and one fix for a regression introduced during 3.19
  merge:

   - Fix inability to discard used space when the thin-pool target is in
     out-of-data-space mode and also transition the thin-pool back to
     write mode once free space is made available.

   - Fix DM core bio-based end_io bug that prevented proper
     post-processing of the error code returned from the block layer.

   - Fix crash in DM thin-pool due to thin device being added to the
     pool's active_thins list before properly initializing the thin
     device's refcount"

* tag 'dm-3.19-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm:
  dm: fix missed error code if .end_io isn't implemented by target_type
  dm thin: fix crash by initializing thin device's refcount and completion earlier
  dm thin: fix missing out-of-data-space to write mode transition if blocks are released
  dm thin: fix inability to discard blocks when in out-of-data-space mode

drivers/md/dm-thin.c

@@ -1127,6 +1127,24 @@ static void schedule_external_copy(struct thin_c *tc, dm_block_t virt_block,
 		schedule_zero(tc, virt_block, data_dest, cell, bio);
 }
 
+static void set_pool_mode(struct pool *pool, enum pool_mode new_mode);
+
+static void check_for_space(struct pool *pool)
+{
+	int r;
+	dm_block_t nr_free;
+
+	if (get_pool_mode(pool) != PM_OUT_OF_DATA_SPACE)
+		return;
+
+	r = dm_pool_get_free_block_count(pool->pmd, &nr_free);
+	if (r)
+		return;
+
+	if (nr_free)
+		set_pool_mode(pool, PM_WRITE);
+}
+
 /*
  * A non-zero return indicates read_only or fail_io mode.
  * Many callers don't care about the return value.
@@ -1141,6 +1159,8 @@ static int commit(struct pool *pool)
 	r = dm_pool_commit_metadata(pool->pmd);
 	if (r)
 		metadata_operation_failed(pool, "dm_pool_commit_metadata", r);
+	else
+		check_for_space(pool);
 
 	return r;
 }
@@ -1159,8 +1179,6 @@ static void check_low_water_mark(struct pool *pool, dm_block_t free_blocks)
 	}
 }
 
-static void set_pool_mode(struct pool *pool, enum pool_mode new_mode);
-
 static int alloc_data_block(struct thin_c *tc, dm_block_t *result)
 {
 	int r;
@@ -2155,7 +2173,7 @@ static void set_pool_mode(struct pool *pool, enum pool_mode new_mode)
 		pool->process_cell = process_cell_read_only;
 		pool->process_discard_cell = process_discard_cell;
 		pool->process_prepared_mapping = process_prepared_mapping;
-		pool->process_prepared_discard = process_prepared_discard_passdown;
+		pool->process_prepared_discard = process_prepared_discard;
 
 		if (!pool->pf.error_if_no_space && no_space_timeout)
 			queue_delayed_work(pool->wq, &pool->no_space_timeout, no_space_timeout);
@@ -3814,6 +3832,8 @@ static int thin_ctr(struct dm_target *ti, unsigned argc, char **argv)
 		r = -EINVAL;
 		goto bad;
 	}
+	atomic_set(&tc->refcount, 1);
+	init_completion(&tc->can_destroy);
 	list_add_tail_rcu(&tc->list, &tc->pool->active_thins);
 	spin_unlock_irqrestore(&tc->pool->lock, flags);
 	/*
@@ -3826,9 +3846,6 @@ static int thin_ctr(struct dm_target *ti, unsigned argc, char **argv)
 
 	dm_put(pool_md);
 
-	atomic_set(&tc->refcount, 1);
-	init_completion(&tc->can_destroy);
-
 	return 0;
 
 bad:

drivers/md/dm.c

@@ -899,7 +899,7 @@ static void disable_write_same(struct mapped_device *md)
 
 static void clone_endio(struct bio *bio, int error)
 {
-	int r = 0;
+	int r = error;
 	struct dm_target_io *tio = container_of(bio, struct dm_target_io, clone);
 	struct dm_io *io = tio->io;
 	struct mapped_device *md = tio->io->md;