Patch "dm: fix reload failure of 0 path multipath mapping on blk-mq devices" has been added to the 4.0-stable tree

This is a note to let you know that I've just added the patch titled

dm: fix reload failure of 0 path multipath mapping on blk-mq devices

to the 4.0-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
dm-fix-reload-failure-of-0-path-multipath-mapping-on-blk-mq-devices.patch
and it can be found in the queue-4.0 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Junichi Nomura <[email protected]>
Date: Fri, 29 May 2015 08:51:03 +0000
Subject: dm: fix reload failure of 0 path multipath mapping on blk-mq devices

From: Junichi Nomura <[email protected]>

commit 15b94a690470038aa08247eedbebbe7e2218d5ee upstream.

dm-multipath accepts 0 path mapping.

  # echo '0 2097152 multipath 0 0 0 0' | dmsetup create newdev

Such a mapping can be used to release underlying devices while still holding requests in its queue until working paths come back.

However, once the multipath device is created over blk-mq devices, it rejects reloading of 0 path mapping:

  # echo '0 2097152 multipath 0 0 1 1 queue-length 0 1 1 /dev/sda 1' \
      | dmsetup create mpath1
  # echo '0 2097152 multipath 0 0 0 0' | dmsetup load mpath1
  device-mapper: reload ioctl on mpath1 failed: Invalid argument
  Command failed

With following kernel message:
device-mapper: ioctl: can't change device type after initial table load.

DM tries to inherit the current table type using dm_table_set_type() but it doesn't work as expected because of unnecessary check about whether the target type is hybrid or not.

Hybrid type is for targets that work as either request-based or bio-based and not required for blk-mq or non blk-mq checking.

---
 drivers/md/dm-table.c |   16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

@@ -823,6 +823,12 @@ void dm_consume_args(struct dm_arg_set *
 }
 EXPORT_SYMBOL(dm_consume_args);
 
+static bool __table_type_request_based(unsigned table_type)
+{
+	return (table_type == DM_TYPE_REQUEST_BASED ||
+		table_type == DM_TYPE_MQ_REQUEST_BASED);
+}
+
 static int dm_table_set_type(struct dm_table *t)
 {
 	unsigned i;

@@ -855,8 +861,7 @@ static int dm_table_set_type(struct dm_t
 		 * Determine the type from the live device.
 		 * Default to bio-based if device is new.
 		 */
-		if (live_md_type == DM_TYPE_REQUEST_BASED ||
-		    live_md_type == DM_TYPE_MQ_REQUEST_BASED)
+		if (__table_type_request_based(live_md_type))
 			request_based = 1;
 		else
 			bio_based = 1;

@@ -906,7 +911,7 @@ static int dm_table_set_type(struct dm_t
 			}
 		t->type = DM_TYPE_MQ_REQUEST_BASED;
 
-	} else if (hybrid && list_empty(devices) && live_md_type != DM_TYPE_NONE) {
+	} else if (list_empty(devices) && __table_type_request_based(live_md_type)) {
 		/* inherit live MD type */
 		t->type = live_md_type;
 

@@ -928,10 +933,7 @@ struct target_type *dm_table_get_immutab
 
 bool dm_table_request_based(struct dm_table *t)
 {
-	unsigned table_type = dm_table_get_type(t);
-
-	return (table_type == DM_TYPE_REQUEST_BASED ||
-		table_type == DM_TYPE_MQ_REQUEST_BASED);
+	return __table_type_request_based(dm_table_get_type(t));
 }
 
 bool dm_table_mq_request_based(struct dm_table *t)

Patches currently in stable-queue which might be from [email protected] are

queue-4.0/dm-fix-reload-failure-of-0-path-multipath-mapping-on-blk-mq-devices.patch