dm snapshot: remove unused dm_snapshot queued_bios_work

dm_snapshot->queued_bios_work isn't used.  Remove ->queued_bios[_work]
from dm_snapshot structure, the flush_queued_bios work function and
ksnapd workqueue.

The DM snapshot changes that were going to use the ksnapd workqueue were
either superseded (fix for origin write races) or never completed
(deallocation of invalid snapshot's memory via workqueue).

Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>

drivers/md/dm-snap.c

@@ -19,7 +19,6 @@
 #include <linux/vmalloc.h>
 #include <linux/log2.h>
 #include <linux/dm-kcopyd.h>
-#include <linux/workqueue.h>
 
 #include "dm-exception-store.h"
 
@@ -106,10 +105,6 @@ struct dm_snapshot {
 
 	struct dm_kcopyd_client *kcopyd_client;
 
-	/* Queue of snapshot writes for ksnapd to flush */
-	struct bio_list queued_bios;
-	struct work_struct queued_bios_work;
-
 	/* Wait for events based on state_bits */
 	unsigned long state_bits;
 
@@ -160,9 +155,6 @@ struct dm_dev *dm_snap_cow(struct dm_snapshot *s)
 }
 EXPORT_SYMBOL(dm_snap_cow);
 
-static struct workqueue_struct *ksnapd;
-static void flush_queued_bios(struct work_struct *work);
-
 static sector_t chunk_to_sector(struct dm_exception_store *store,
 				chunk_t chunk)
 {
@@ -1153,9 +1145,6 @@ static int snapshot_ctr(struct dm_target *ti, unsigned int argc, char **argv)
 
 	spin_lock_init(&s->tracked_chunk_lock);
 
-	bio_list_init(&s->queued_bios);
-	INIT_WORK(&s->queued_bios_work, flush_queued_bios);
-
 	ti->private = s;
 	ti->num_flush_requests = num_flush_requests;
 
@@ -1279,8 +1268,6 @@ static void snapshot_dtr(struct dm_target *ti)
 	struct dm_snapshot *s = ti->private;
 	struct dm_snapshot *snap_src = NULL, *snap_dest = NULL;
 
-	flush_workqueue(ksnapd);
-
 	down_read(&_origins_lock);
 	/* Check whether exception handover must be cancelled */
 	(void) __find_snapshots_sharing_cow(s, &snap_src, &snap_dest, NULL);
@@ -1342,20 +1329,6 @@ static void flush_bios(struct bio *bio)
 	}
 }
 
-static void flush_queued_bios(struct work_struct *work)
-{
-	struct dm_snapshot *s =
-		container_of(work, struct dm_snapshot, queued_bios_work);
-	struct bio *queued_bios;
-	unsigned long flags;
-
-	spin_lock_irqsave(&s->pe_lock, flags);
-	queued_bios = bio_list_get(&s->queued_bios);
-	spin_unlock_irqrestore(&s->pe_lock, flags);
-
-	flush_bios(queued_bios);
-}
-
 static int do_origin(struct dm_dev *origin, struct bio *bio);
 
 /*
@@ -2291,17 +2264,8 @@ static int __init dm_snapshot_init(void)
 		goto bad_tracked_chunk_cache;
 	}
 
-	ksnapd = create_singlethread_workqueue("ksnapd");
-	if (!ksnapd) {
-		DMERR("Failed to create ksnapd workqueue.");
-		r = -ENOMEM;
-		goto bad_pending_pool;
-	}
-
 	return 0;
 
-bad_pending_pool:
-	kmem_cache_destroy(tracked_chunk_cache);
 bad_tracked_chunk_cache:
 	kmem_cache_destroy(pending_cache);
 bad_pending_cache:
@@ -2322,8 +2286,6 @@ bad_register_snapshot_target:
 
 static void __exit dm_snapshot_exit(void)
 {
-	destroy_workqueue(ksnapd);
-
 	dm_unregister_target(&snapshot_target);
 	dm_unregister_target(&origin_target);
 	dm_unregister_target(&merge_target);