[PATCH 2/2 v2] dm: only initialize full request_queue for request-based device

[Mike Snitzer <snitzer@redhat.com>]

Revert back to only allocating a minimalist request_queue structure
initially (needed for both bio and request-based DM).  Initialization of
a full request_queue (request_fn, elevator, etc) is deferred until it is
known that the DM device is request-based.

dm_init_request_based_queue is now called at the end of a request-based
DM device's table load.

Otherwise bio-based DM devices will have an elevator, request_fn, etc.
As a result bio-based DM devices had an 'iosched/' tree as well as a
'scheduler' other than "none" in sysfs.

Signed-off-by: Mike Snitzer <snitzer@redhat.com>
---
 drivers/md/dm-table.c |    5 ++++
 drivers/md/dm.c       |   64 +++++++++++++++++++++++++++++++++++-------------
 drivers/md/dm.h       |    2 +
 3 files changed, 53 insertions(+), 18 deletions(-)

diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index 9924ea2..64a8578 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -829,6 +829,11 @@ int dm_table_set_type(struct dm_table *t)
 		return -EINVAL;
 	}
 
+	if (!dm_init_request_based_queue(t->md)) {
+		DMWARN("Cannot initialize queue for Request-based dm");
+		return -EINVAL;
+	}
+
 	t->type = DM_TYPE_REQUEST_BASED;
 
 	return 0;
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index d21e128..b2171be 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1886,22 +1886,10 @@ static struct mapped_device *alloc_dev(int minor)
 	INIT_LIST_HEAD(&md->uevent_list);
 	spin_lock_init(&md->uevent_lock);
 
-	md->queue = blk_init_queue(dm_request_fn, NULL);
+	md->queue = blk_alloc_queue(GFP_KERNEL);
 	if (!md->queue)
 		goto bad_queue;
 
-	/*
-	 * Request-based dm devices cannot be stacked on top of bio-based dm
-	 * devices.  The type of this dm device has not been decided yet,
-	 * although we initialized the queue using blk_init_queue().
-	 * The type is decided at the first table loading time.
-	 * To prevent problematic device stacking, clear the queue flag
-	 * for request stacking support until then.
-	 *
-	 * This queue is new, so no concurrency on the queue_flags.
-	 */
-	queue_flag_clear_unlocked(QUEUE_FLAG_STACKABLE, md->queue);
-	md->saved_make_request_fn = md->queue->make_request_fn;
 	md->queue->queuedata = md;
 	md->queue->backing_dev_info.congested_fn = dm_any_congested;
 	md->queue->backing_dev_info.congested_data = md;
@@ -1909,11 +1897,6 @@ static struct mapped_device *alloc_dev(int minor)
 	blk_queue_bounce_limit(md->queue, BLK_BOUNCE_ANY);
 	md->queue->unplug_fn = dm_unplug_all;
 	blk_queue_merge_bvec(md->queue, dm_merge_bvec);
-	blk_queue_softirq_done(md->queue, dm_softirq_done);
-	blk_queue_prep_rq(md->queue, dm_prep_fn);
-	blk_queue_lld_busy(md->queue, dm_lld_busy);
-	blk_queue_ordered(md->queue, QUEUE_ORDERED_DRAIN_FLUSH,
-			  dm_rq_prepare_flush);
 
 	md->disk = alloc_disk(1);
 	if (!md->disk)
@@ -1968,6 +1951,51 @@ bad_module_get:
 	return NULL;
 }
 
+/*
+ * Fully initialize the request_queue (elevator, ->request_fn, etc).
+ */
+int dm_init_request_based_queue(struct mapped_device *md)
+{
+	struct request_queue *q = NULL;
+
+	if (!md->queue)
+		return 0;
+
+	/*
+	 * Avoid re-initializing the queue (and leaking the existing
+	 * elevator) if dm_init_request_based_queue() was already used.
+	 */
+	if (!md->queue->elevator) {
+		/* Fully initialize the queue */
+		q = blk_init_allocated_queue(md->queue, dm_request_fn, NULL);
+		if (!q)
+			return 0;
+		md->queue = q;
+		md->saved_make_request_fn = md->queue->make_request_fn;
+		blk_queue_make_request(md->queue, dm_request);
+		elv_register_queue(md->queue);
+	}
+
+	/*
+	 * Request-based dm devices cannot be stacked on top of bio-based dm
+	 * devices.  The type of this dm device has not been decided yet.
+	 * The type is decided at the first table loading time.
+	 * To prevent problematic device stacking, clear the queue flag
+	 * for request stacking support until then.
+	 *
+	 * This queue is new, so no concurrency on the queue_flags.
+	 */
+	queue_flag_clear_unlocked(QUEUE_FLAG_STACKABLE, md->queue);
+
+	blk_queue_softirq_done(md->queue, dm_softirq_done);
+	blk_queue_prep_rq(md->queue, dm_prep_fn);
+	blk_queue_lld_busy(md->queue, dm_lld_busy);
+	blk_queue_ordered(md->queue, QUEUE_ORDERED_DRAIN_FLUSH,
+			  dm_rq_prepare_flush);
+
+	return 1;
+}
+
 static void unlock_fs(struct mapped_device *md);
 
 static void free_dev(struct mapped_device *md)
diff --git a/drivers/md/dm.h b/drivers/md/dm.h
index bad1724..489feba 100644
--- a/drivers/md/dm.h
+++ b/drivers/md/dm.h
@@ -113,6 +113,8 @@ void dm_sysfs_exit(struct mapped_device *md);
 struct kobject *dm_kobject(struct mapped_device *md);
 struct mapped_device *dm_get_from_kobject(struct kobject *kobj);
 
+int dm_init_request_based_queue(struct mapped_device *md);
+
 /*
  * Targets for linear and striped mappings
  */