Merge tag 'for-5.3/dm-changes' of...

Merge tag 'for-5.3/dm-changes' of git://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm

Pull device mapper updates from Mike Snitzer:

 - Add encrypted byte-offset initialization vector (eboiv) to DM crypt.

 - Add optional discard features to DM snapshot which allow freeing
   space from a DM device whose free space was exhausted.

 - Various small improvements to use struct_size() and kzalloc().

 - Fix to check if DM thin metadata is in fail_io mode before attempting
   to update the superblock to set the needs_check flag. Otherwise the
   DM thin-pool can hang.

 - Fix DM bufio shrinker's potential for ABBA recursion deadlock with DM
   thin provisioning on loop usecase.

* tag 'for-5.3/dm-changes' of git://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm:
  dm bufio: fix deadlock with loop device
  dm snapshot: add optional discard support features
  dm crypt: implement eboiv - encrypted byte-offset initialization vector
  dm crypt: remove obsolete comment about plumb IV
  dm crypt: wipe private IV struct after key invalid flag is set
  dm integrity: use kzalloc() instead of kmalloc() + memset()
  dm: update stale comment in end_clone_bio()
  dm log writes: fix incorrect comment about the logged sequence example
  dm log writes: use struct_size() to calculate size of pending_block
  dm crypt: use struct_size() when allocating encryption context
  dm integrity: always set version on superblock update
  dm thin metadata: check if in fail_io mode when setting needs_check

Documentation/device-mapper/snapshot.rst

@@ -32,6 +32,7 @@ its visible content unchanged, at least until the <COW device> fills up.
 
 
 -  snapshot <origin> <COW device> <persistent?> <chunksize>
+   [<# feature args> [<arg>]*]
 
 A snapshot of the <origin> block device is created. Changed chunks of
 <chunksize> sectors will be stored on the <COW device>.  Writes will
@@ -54,8 +55,23 @@ When loading or unloading the snapshot target, the corresponding
 snapshot-origin or snapshot-merge target must be suspended. A failure to
 suspend the origin target could result in data corruption.
 
+Optional features:
 
-* snapshot-merge <origin> <COW device> <persistent> <chunksize>
+   discard_zeroes_cow - a discard issued to the snapshot device that
+   maps to entire chunks to will zero the corresponding exception(s) in
+   the snapshot's exception store.
+
+   discard_passdown_origin - a discard to the snapshot device is passed
+   down to the snapshot-origin's underlying device.  This doesn't cause
+   copy-out to the snapshot exception store because the snapshot-origin
+   target is bypassed.
+
+   The discard_passdown_origin feature depends on the discard_zeroes_cow
+   feature being enabled.
+
+
+-  snapshot-merge <origin> <COW device> <persistent> <chunksize>
+   [<# feature args> [<arg>]*]
 
 takes the same table arguments as the snapshot target except it only
 works with persistent snapshots.  This target assumes the role of the

drivers/md/dm-bufio.c

@@ -1599,9 +1599,7 @@ dm_bufio_shrink_scan(struct shrinker *shrink, struct shrink_control *sc)
 	unsigned long freed;
 
 	c = container_of(shrink, struct dm_bufio_client, shrinker);
-	if (sc->gfp_mask & __GFP_FS)
-		dm_bufio_lock(c);
-	else if (!dm_bufio_trylock(c))
+	if (!dm_bufio_trylock(c))
 		return SHRINK_STOP;
 
 	freed  = __scan(c, sc->nr_to_scan, sc->gfp_mask);

drivers/md/dm-crypt.c

@@ -120,6 +120,10 @@ struct iv_tcw_private {
 	u8 *whitening;
 };
 
+struct iv_eboiv_private {
+	struct crypto_cipher *tfm;
+};
+
 /*
  * Crypt: maps a linear range of a block device
  * and encrypts / decrypts at the same time.
@@ -159,6 +163,7 @@ struct crypt_config {
 		struct iv_benbi_private benbi;
 		struct iv_lmk_private lmk;
 		struct iv_tcw_private tcw;
+		struct iv_eboiv_private eboiv;
 	} iv_gen_private;
 	u64 iv_offset;
 	unsigned int iv_size;
@@ -291,8 +296,9 @@ static struct crypto_aead *any_tfm_aead(struct crypt_config *cc)
  *       Note that this encryption scheme is vulnerable to watermarking attacks
  *       and should be used for old compatible containers access only.
  *
- * plumb: unimplemented, see:
- * http://article.gmane.org/gmane.linux.kernel.device-mapper.dm-crypt/454
+ * eboiv: Encrypted byte-offset IV (used in Bitlocker in CBC mode)
+ *        The IV is encrypted little-endian byte-offset (with the same key
+ *        and cipher as the volume).
  */
 
 static int crypt_iv_plain_gen(struct crypt_config *cc, u8 *iv,
@@ -841,6 +847,67 @@ static int crypt_iv_random_gen(struct crypt_config *cc, u8 *iv,
 	return 0;
 }
 
+static void crypt_iv_eboiv_dtr(struct crypt_config *cc)
+{
+	struct iv_eboiv_private *eboiv = &cc->iv_gen_private.eboiv;
+
+	crypto_free_cipher(eboiv->tfm);
+	eboiv->tfm = NULL;
+}
+
+static int crypt_iv_eboiv_ctr(struct crypt_config *cc, struct dm_target *ti,
+			    const char *opts)
+{
+	struct iv_eboiv_private *eboiv = &cc->iv_gen_private.eboiv;
+	struct crypto_cipher *tfm;
+
+	tfm = crypto_alloc_cipher(cc->cipher, 0, 0);
+	if (IS_ERR(tfm)) {
+		ti->error = "Error allocating crypto tfm for EBOIV";
+		return PTR_ERR(tfm);
+	}
+
+	if (crypto_cipher_blocksize(tfm) != cc->iv_size) {
+		ti->error = "Block size of EBOIV cipher does "
+			    "not match IV size of block cipher";
+		crypto_free_cipher(tfm);
+		return -EINVAL;
+	}
+
+	eboiv->tfm = tfm;
+	return 0;
+}
+
+static int crypt_iv_eboiv_init(struct crypt_config *cc)
+{
+	struct iv_eboiv_private *eboiv = &cc->iv_gen_private.eboiv;
+	int err;
+
+	err = crypto_cipher_setkey(eboiv->tfm, cc->key, cc->key_size);
+	if (err)
+		return err;
+
+	return 0;
+}
+
+static int crypt_iv_eboiv_wipe(struct crypt_config *cc)
+{
+	/* Called after cc->key is set to random key in crypt_wipe() */
+	return crypt_iv_eboiv_init(cc);
+}
+
+static int crypt_iv_eboiv_gen(struct crypt_config *cc, u8 *iv,
+			    struct dm_crypt_request *dmreq)
+{
+	struct iv_eboiv_private *eboiv = &cc->iv_gen_private.eboiv;
+
+	memset(iv, 0, cc->iv_size);
+	*(__le64 *)iv = cpu_to_le64(dmreq->iv_sector * cc->sector_size);
+	crypto_cipher_encrypt_one(eboiv->tfm, iv, iv);
+
+	return 0;
+}
+
 static const struct crypt_iv_operations crypt_iv_plain_ops = {
 	.generator = crypt_iv_plain_gen
 };
@@ -893,6 +960,14 @@ static struct crypt_iv_operations crypt_iv_random_ops = {
 	.generator = crypt_iv_random_gen
 };
 
+static struct crypt_iv_operations crypt_iv_eboiv_ops = {
+	.ctr	   = crypt_iv_eboiv_ctr,
+	.dtr	   = crypt_iv_eboiv_dtr,
+	.init	   = crypt_iv_eboiv_init,
+	.wipe	   = crypt_iv_eboiv_wipe,
+	.generator = crypt_iv_eboiv_gen
+};
+
 /*
  * Integrity extensions
  */
@@ -2158,6 +2233,14 @@ static int crypt_wipe_key(struct crypt_config *cc)
 
 	clear_bit(DM_CRYPT_KEY_VALID, &cc->flags);
 	get_random_bytes(&cc->key, cc->key_size);
+
+	/* Wipe IV private keys */
+	if (cc->iv_gen_ops && cc->iv_gen_ops->wipe) {
+		r = cc->iv_gen_ops->wipe(cc);
+		if (r)
+			return r;
+	}
+
 	kzfree(cc->key_string);
 	cc->key_string = NULL;
 	r = crypt_setkey(cc);
@@ -2288,6 +2371,8 @@ static int crypt_ctr_ivmode(struct dm_target *ti, const char *ivmode)
 		cc->iv_gen_ops = &crypt_iv_benbi_ops;
 	else if (strcmp(ivmode, "null") == 0)
 		cc->iv_gen_ops = &crypt_iv_null_ops;
+	else if (strcmp(ivmode, "eboiv") == 0)
+		cc->iv_gen_ops = &crypt_iv_eboiv_ops;
 	else if (strcmp(ivmode, "lmk") == 0) {
 		cc->iv_gen_ops = &crypt_iv_lmk_ops;
 		/*
@@ -2699,7 +2784,7 @@ static int crypt_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 		return -EINVAL;
 	}
 
-	cc = kzalloc(sizeof(*cc) + key_size * sizeof(u8), GFP_KERNEL);
+	cc = kzalloc(struct_size(cc, key, key_size), GFP_KERNEL);
 	if (!cc) {
 		ti->error = "Cannot allocate encryption context";
 		return -ENOMEM;
@@ -3050,14 +3135,8 @@ static int crypt_message(struct dm_target *ti, unsigned argc, char **argv,
 				memset(cc->key, 0, cc->key_size * sizeof(u8));
 			return ret;
 		}
-		if (argc == 2 && !strcasecmp(argv[1], "wipe")) {
-			if (cc->iv_gen_ops && cc->iv_gen_ops->wipe) {
-				ret = cc->iv_gen_ops->wipe(cc);
-				if (ret)
-					return ret;
-			}
+		if (argc == 2 && !strcasecmp(argv[1], "wipe"))
 			return crypt_wipe_key(cc);
-		}
 	}
 
 error:
@@ -3094,7 +3173,7 @@ static void crypt_io_hints(struct dm_target *ti, struct queue_limits *limits)
 
 static struct target_type crypt_target = {
 	.name   = "crypt",
-	.version = {1, 18, 1},
+	.version = {1, 19, 0},
 	.module = THIS_MODULE,
 	.ctr    = crypt_ctr,
 	.dtr    = crypt_dtr,

drivers/md/dm-integrity.c

@@ -476,6 +476,9 @@ static int sync_rw_sb(struct dm_integrity_c *ic, int op, int op_flags)
 	io_loc.sector = ic->start;
 	io_loc.count = SB_SECTORS;
 
+	if (op == REQ_OP_WRITE)
+		sb_set_version(ic);
+
 	return dm_io(&io_req, 1, &io_loc, NULL);
 }
 
@@ -2317,7 +2320,6 @@ static void recalc_write_super(struct dm_integrity_c *ic)
 	if (dm_integrity_failed(ic))
 		return;
 
-	sb_set_version(ic);
 	r = sync_rw_sb(ic, REQ_OP_WRITE, 0);
 	if (unlikely(r))
 		dm_integrity_io_error(ic, "writing superblock", r);
@@ -3358,7 +3360,7 @@ static int create_journal(struct dm_integrity_c *ic, char **error)
 				goto bad;
 			}
 
-			crypt_iv = kmalloc(ivsize, GFP_KERNEL);
+			crypt_iv = kzalloc(ivsize, GFP_KERNEL);
 			if (!crypt_iv) {
 				*error = "Could not allocate iv";
 				r = -ENOMEM;
@@ -3387,7 +3389,6 @@ static int create_journal(struct dm_integrity_c *ic, char **error)
 				sg_set_buf(&sg[i], va, PAGE_SIZE);
 			}
 			sg_set_buf(&sg[i], &ic->commit_ids, sizeof ic->commit_ids);
-			memset(crypt_iv, 0x00, ivsize);
 
 			skcipher_request_set_crypt(req, sg, sg,
 						   PAGE_SIZE * ic->journal_pages + sizeof ic->commit_ids, crypt_iv);

drivers/md/dm-log-writes.c

@@ -40,7 +40,7 @@
  *
  * Would result in the log looking like this:
  *
- * c,a,flush,fuad,b,<other writes>,<next flush>
+ * c,a,b,flush,fuad,<other writes>,<next flush>
  *
  * This is meant to help expose problems where file systems do not properly wait
  * on data being written before invoking a FLUSH.  FUA bypasses cache so once it
@@ -699,7 +699,7 @@ static int log_writes_map(struct dm_target *ti, struct bio *bio)
 	if (discard_bio)
 		alloc_size = sizeof(struct pending_block);
 	else
-		alloc_size = sizeof(struct pending_block) + sizeof(struct bio_vec) * bio_segments(bio);
+		alloc_size = struct_size(block, vecs, bio_segments(bio));
 
 	block = kzalloc(alloc_size, GFP_NOIO);
 	if (!block) {

drivers/md/dm-rq.c

@@ -115,7 +115,7 @@ static void end_clone_bio(struct bio *clone)
 
 	/*
 	 * Update the original request.
-	 * Do not use blk_end_request() here, because it may complete
+	 * Do not use blk_mq_end_request() here, because it may complete
 	 * the original request before the clone, and break the ordering.
 	 */
 	if (is_last)

drivers/md/dm-snap.c

 /*
- * dm-snapshot.c
- *
  * Copyright (C) 2001-2002 Sistina Software (UK) Limited.
  *
  * This file is released under the GPL.
@@ -134,7 +132,10 @@ struct dm_snapshot {
 	 * - I/O error while merging
 	 *	=> stop merging; set merge_failed; process I/O normally.
 	 */
-	int merge_failed;
+	bool merge_failed:1;
+
+	bool discard_zeroes_cow:1;
+	bool discard_passdown_origin:1;
 
 	/*
 	 * Incoming bios that overlap with chunks being merged must wait
@@ -1173,12 +1174,64 @@ static void stop_merge(struct dm_snapshot *s)
 	clear_bit(SHUTDOWN_MERGE, &s->state_bits);
 }
 
+static int parse_snapshot_features(struct dm_arg_set *as, struct dm_snapshot *s,
+				   struct dm_target *ti)
+{
+	int r;
+	unsigned argc;
+	const char *arg_name;
+
+	static const struct dm_arg _args[] = {
+		{0, 2, "Invalid number of feature arguments"},
+	};
+
+	/*
+	 * No feature arguments supplied.
+	 */
+	if (!as->argc)
+		return 0;
+
+	r = dm_read_arg_group(_args, as, &argc, &ti->error);
+	if (r)
+		return -EINVAL;
+
+	while (argc && !r) {
+		arg_name = dm_shift_arg(as);
+		argc--;
+
+		if (!strcasecmp(arg_name, "discard_zeroes_cow"))
+			s->discard_zeroes_cow = true;
+
+		else if (!strcasecmp(arg_name, "discard_passdown_origin"))
+			s->discard_passdown_origin = true;
+
+		else {
+			ti->error = "Unrecognised feature requested";
+			r = -EINVAL;
+			break;
+		}
+	}
+
+	if (!s->discard_zeroes_cow && s->discard_passdown_origin) {
+		/*
+		 * TODO: really these are disjoint.. but ti->num_discard_bios
+		 * and dm_bio_get_target_bio_nr() require rigid constraints.
+		 */
+		ti->error = "discard_passdown_origin feature depends on discard_zeroes_cow";
+		r = -EINVAL;
+	}
+
+	return r;
+}
+
 /*
- * Construct a snapshot mapping: <origin_dev> <COW-dev> <p|po|n> <chunk-size>
+ * Construct a snapshot mapping:
+ * <origin_dev> <COW-dev> <p|po|n> <chunk-size> [<# feature args> [<arg>]*]
  */
 static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 {
 	struct dm_snapshot *s;
+	struct dm_arg_set as;
 	int i;
 	int r = -EINVAL;
 	char *origin_path, *cow_path;
@@ -1186,8 +1239,8 @@ static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 	unsigned args_used, num_flush_bios = 1;
 	fmode_t origin_mode = FMODE_READ;
 
-	if (argc != 4) {
-		ti->error = "requires exactly 4 arguments";
+	if (argc < 4) {
+		ti->error = "requires 4 or more arguments";
 		r = -EINVAL;
 		goto bad;
 	}
@@ -1204,6 +1257,13 @@ static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 		goto bad;
 	}
 
+	as.argc = argc;
+	as.argv = argv;
+	dm_consume_args(&as, 4);
+	r = parse_snapshot_features(&as, s, ti);
+	if (r)
+		goto bad_features;
+
 	origin_path = argv[0];
 	argv++;
 	argc--;
@@ -1289,6 +1349,8 @@ static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 
 	ti->private = s;
 	ti->num_flush_bios = num_flush_bios;
+	if (s->discard_zeroes_cow)
+		ti->num_discard_bios = (s->discard_passdown_origin ? 2 : 1);
 	ti->per_io_data_size = sizeof(struct dm_snap_tracked_chunk);
 
 	/* Add snapshot to the list of snapshots for this origin */
@@ -1336,29 +1398,22 @@ static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 
 bad_read_metadata:
 	unregister_snapshot(s);
-
 bad_load_and_register:
 	mempool_exit(&s->pending_pool);
-
 bad_pending_pool:
 	dm_kcopyd_client_destroy(s->kcopyd_client);
-
 bad_kcopyd:
 	dm_exception_table_exit(&s->pending, pending_cache);
 	dm_exception_table_exit(&s->complete, exception_cache);
-
 bad_hash_tables:
 	dm_exception_store_destroy(s->store);
-
 bad_store:
 	dm_put_device(ti, s->cow);
-
 bad_cow:
 	dm_put_device(ti, s->origin);
-
 bad_origin:
+bad_features:
 	kfree(s);
-
 bad:
 	return r;
 }
@@ -1806,6 +1861,37 @@ static void remap_exception(struct dm_snapshot *s, struct dm_exception *e,
 		(bio->bi_iter.bi_sector & s->store->chunk_mask);
 }
 
+static void zero_callback(int read_err, unsigned long write_err, void *context)
+{
+	struct bio *bio = context;
+	struct dm_snapshot *s = bio->bi_private;
+
+	up(&s->cow_count);
+	bio->bi_status = write_err ? BLK_STS_IOERR : 0;
+	bio_endio(bio);
+}
+
+static void zero_exception(struct dm_snapshot *s, struct dm_exception *e,
+			   struct bio *bio, chunk_t chunk)
+{
+	struct dm_io_region dest;
+
+	dest.bdev = s->cow->bdev;
+	dest.sector = bio->bi_iter.bi_sector;
+	dest.count = s->store->chunk_size;
+
+	down(&s->cow_count);
+	WARN_ON_ONCE(bio->bi_private);
+	bio->bi_private = s;
+	dm_kcopyd_zero(s->kcopyd_client, 1, &dest, 0, zero_callback, bio);
+}
+
+static bool io_overlaps_chunk(struct dm_snapshot *s, struct bio *bio)
+{
+	return bio->bi_iter.bi_size ==
+		(s->store->chunk_size << SECTOR_SHIFT);
+}
+
 static int snapshot_map(struct dm_target *ti, struct bio *bio)
 {
 	struct dm_exception *e;
@@ -1839,10 +1925,43 @@ static int snapshot_map(struct dm_target *ti, struct bio *bio)
 		goto out_unlock;
 	}
 
+	if (unlikely(bio_op(bio) == REQ_OP_DISCARD)) {
+		if (s->discard_passdown_origin && dm_bio_get_target_bio_nr(bio)) {
+			/*
+			 * passdown discard to origin (without triggering
+			 * snapshot exceptions via do_origin; doing so would
+			 * defeat the goal of freeing space in origin that is
+			 * implied by the "discard_passdown_origin" feature)
+			 */
+			bio_set_dev(bio, s->origin->bdev);
+			track_chunk(s, bio, chunk);
+			goto out_unlock;
+		}
+		/* discard to snapshot (target_bio_nr == 0) zeroes exceptions */
+	}
+
 	/* If the block is already remapped - use that, else remap it */
 	e = dm_lookup_exception(&s->complete, chunk);
 	if (e) {
 		remap_exception(s, e, bio, chunk);
+		if (unlikely(bio_op(bio) == REQ_OP_DISCARD) &&
+		    io_overlaps_chunk(s, bio)) {
+			dm_exception_table_unlock(&lock);
+			up_read(&s->lock);
+			zero_exception(s, e, bio, chunk);
+			r = DM_MAPIO_SUBMITTED; /* discard is not issued */
+			goto out;
+		}
+		goto out_unlock;
+	}
+
+	if (unlikely(bio_op(bio) == REQ_OP_DISCARD)) {
+		/*
+		 * If no exception exists, complete discard immediately
+		 * otherwise it'll trigger copy-out.
+		 */
+		bio_endio(bio);
+		r = DM_MAPIO_SUBMITTED;
 		goto out_unlock;
 	}
 
@@ -1890,9 +2009,7 @@ static int snapshot_map(struct dm_target *ti, struct bio *bio)
 
 		r = DM_MAPIO_SUBMITTED;
 
-		if (!pe->started &&
-		    bio->bi_iter.bi_size ==
-		    (s->store->chunk_size << SECTOR_SHIFT)) {
+		if (!pe->started && io_overlaps_chunk(s, bio)) {
 			pe->started = 1;
 
 			dm_exception_table_unlock(&lock);
@@ -2138,6 +2255,7 @@ static void snapshot_status(struct dm_target *ti, status_type_t type,
 {
 	unsigned sz = 0;
 	struct dm_snapshot *snap = ti->private;
+	unsigned num_features;
 
 	switch (type) {
 	case STATUSTYPE_INFO:
@@ -2178,8 +2296,16 @@ static void snapshot_status(struct dm_target *ti, status_type_t type,
 		 * make sense.
 		 */
 		DMEMIT("%s %s", snap->origin->name, snap->cow->name);
-		snap->store->type->status(snap->store, type, result + sz,
-					  maxlen - sz);
+		sz += snap->store->type->status(snap->store, type, result + sz,
+						maxlen - sz);
+		num_features = snap->discard_zeroes_cow + snap->discard_passdown_origin;
+		if (num_features) {
+			DMEMIT(" %u", num_features);
+			if (snap->discard_zeroes_cow)
+				DMEMIT(" discard_zeroes_cow");
+			if (snap->discard_passdown_origin)
+				DMEMIT(" discard_passdown_origin");
+		}
 		break;
 	}
 }
@@ -2198,6 +2324,22 @@ static int snapshot_iterate_devices(struct dm_target *ti,
 	return r;
 }
 
+static void snapshot_io_hints(struct dm_target *ti, struct queue_limits *limits)
+{
+	struct dm_snapshot *snap = ti->private;
+
+	if (snap->discard_zeroes_cow) {
+		struct dm_snapshot *snap_src = NULL, *snap_dest = NULL;
+
+		(void) __find_snapshots_sharing_cow(snap, &snap_src, &snap_dest, NULL);
+		if (snap_src && snap_dest)
+			snap = snap_src;
+
+		/* All discards are split on chunk_size boundary */
+		limits->discard_granularity = snap->store->chunk_size;
+		limits->max_discard_sectors = snap->store->chunk_size;
+	}
+}
 
 /*-----------------------------------------------------------------
  * Origin methods
@@ -2522,7 +2664,7 @@ static struct target_type origin_target = {
 
 static struct target_type snapshot_target = {
 	.name    = "snapshot",
-	.version = {1, 15, 0},
+	.version = {1, 16, 0},
 	.module  = THIS_MODULE,
 	.ctr     = snapshot_ctr,
 	.dtr     = snapshot_dtr,
@@ -2532,11 +2674,12 @@ static struct target_type snapshot_target = {
 	.resume  = snapshot_resume,
 	.status  = snapshot_status,
 	.iterate_devices = snapshot_iterate_devices,
+	.io_hints = snapshot_io_hints,
 };
 
 static struct target_type merge_target = {
 	.name    = dm_snapshot_merge_target_name,
-	.version = {1, 4, 0},
+	.version = {1, 5, 0},
 	.module  = THIS_MODULE,
 	.ctr     = snapshot_ctr,
 	.dtr     = snapshot_dtr,
@@ -2547,6 +2690,7 @@ static struct target_type merge_target = {
 	.resume  = snapshot_merge_resume,
 	.status  = snapshot_status,
 	.iterate_devices = snapshot_iterate_devices,
+	.io_hints = snapshot_io_hints,
 };
 
 static int __init dm_snapshot_init(void)

drivers/md/dm-thin-metadata.c

@@ -2046,16 +2046,19 @@ int dm_pool_register_metadata_threshold(struct dm_pool_metadata *pmd,
 
 int dm_pool_metadata_set_needs_check(struct dm_pool_metadata *pmd)
 {
-	int r;
+	int r = -EINVAL;
 	struct dm_block *sblock;
 	struct thin_disk_superblock *disk_super;
 
 	pmd_write_lock(pmd);
+	if (pmd->fail_io)
+		goto out;
+
 	pmd->flags |= THIN_METADATA_NEEDS_CHECK_FLAG;
 
 	r = superblock_lock(pmd, &sblock);
 	if (r) {
-		DMERR("couldn't read superblock");
+		DMERR("couldn't lock superblock");
 		goto out;
 	}