3.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Joe Thornber <redacted>

commit 2a7eaea02b99b6e267b1e89c79acc6e9a51cee3b upstream.

You can't modify the metadata in these modes.  It's better to fail these
messages immediately than let the block-manager deny write locks on
metadata blocks.  Otherwise these failed metadata changes will trigger
'needs_check' to get set in the metadata superblock -- requiring repair
using the thin_check utility.

Signed-off-by: Joe Thornber <redacted>
Signed-off-by: Mike Snitzer <redacted>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 drivers/md/dm-thin.c |    6 ++++++
 1 file changed, 6 insertions(+)

--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c

@@ -2978,6 +2978,12 @@ static int pool_message(struct dm_target
 	struct pool_c *pt = ti->private;
 	struct pool *pool = pt->pool;
 
+	if (get_pool_mode(pool) >= PM_READ_ONLY) {
+		DMERR("%s: unable to service pool target messages in READ_ONLY or FAIL mode",
+		      dm_device_name(pool->pool_md));
+		return -EINVAL;
+	}
+
 	if (!strcasecmp(argv[0], "create_thin"))
 		r = process_create_thin_mesg(argc, argv, pool);