dm: remove the pending variable

Index: linux-2.6/drivers/md/dm-core.h
===================================================================
@@ -65,7 +65,6 @@ struct mapped_device {
 	 */
 	struct work_struct work;
 	wait_queue_head_t wait;
-	atomic_t pending[2];
 	spinlock_t deferred_lock;
 	struct bio_list deferred;
 

Index: linux-2.6/drivers/md/dm.c
===================================================================
@@ -597,23 +597,20 @@ static void free_tio(struct dm_target_io
 
 int md_in_flight(struct mapped_device *md)
 {
-	return atomic_read(&md->pending[READ]) +
-	       atomic_read(&md->pending[WRITE]);
+	return atomic_read(&dm_disk(md)->part0.in_flight[READ]) +
+	       atomic_read(&dm_disk(md)->part0.in_flight[WRITE]);
 }
 
 static void start_io_acct(struct dm_io *io)
 {
 	struct mapped_device *md = io->md;
 	struct bio *bio = io->orig_bio;
-	int rw = bio_data_dir(bio);
 
 	io->start_time = jiffies;
 
 	generic_start_io_acct(md->queue, bio_op(bio), bio_sectors(bio),
 			      &dm_disk(md)->part0);
 
-	atomic_inc(&md->pending[rw]);
-
 	if (unlikely(dm_stats_used(&md->stats)))
 		dm_stats_account_io(&md->stats, bio_data_dir(bio),
 				    bio->bi_iter.bi_sector, bio_sectors(bio),

@@ -625,27 +622,30 @@ static void end_io_acct(struct dm_io *io
 	struct mapped_device *md = io->md;
 	struct bio *bio = io->orig_bio;
 	unsigned long duration = jiffies - io->start_time;
-	int pending;
-	int rw = bio_data_dir(bio);
 
+	/*
+	 * make sure that atomic_dec in generic_end_io_acct is not reordered
+	 * with previous writes
+	 */
+	smp_mb__before_atomic();
 	generic_end_io_acct(md->queue, bio_op(bio), &dm_disk(md)->part0,
 			    io->start_time);
+	/*
+	 * generic_end_io_acct does atomic_dec, this barrier makes sure that
+	 * atomic_dec is not reordered with waitqueue_active
+	 */
+	smp_mb__after_atomic();
 
 	if (unlikely(dm_stats_used(&md->stats)))
 		dm_stats_account_io(&md->stats, bio_data_dir(bio),
 				    bio->bi_iter.bi_sector, bio_sectors(bio),
 				    true, duration, &io->stats_aux);
 
-	/*
-	 * After this is decremented the bio must not be touched if it is
-	 * a flush.
-	 */
-	pending = atomic_dec_return(&md->pending[rw]);
-	pending += atomic_read(&md->pending[rw^0x1]);
-
 	/* nudge anyone waiting on suspend queue */
-	if (!pending)
-		wake_up(&md->wait);
+	if (unlikely(waitqueue_active(&md->wait))) {
+		if (!md_in_flight(md))
+			wake_up(&md->wait);
+	}
 }
 
 /*

@@ -1899,8 +1899,6 @@ static struct mapped_device *alloc_dev(i
 	if (!md->disk)
 		goto bad;
 
-	atomic_set(&md->pending[0], 0);
-	atomic_set(&md->pending[1], 0);
 	init_waitqueue_head(&md->wait);
 	INIT_WORK(&md->work, dm_wq_work);
 	init_waitqueue_head(&md->eventq);

Index: linux-2.6/drivers/md/dm-rq.c
===================================================================
@@ -182,7 +182,7 @@ static void rq_completed(struct mapped_d
 	struct request_queue *q = md->queue;
 	unsigned long flags;
 
-	atomic_dec(&md->pending[rw]);
+	atomic_dec(&dm_disk(md)->part0.in_flight[rw]);
 
 	/* nudge anyone waiting on suspend queue */
 	if (!md_in_flight(md))

@@ -536,7 +536,7 @@ static void dm_start_request(struct mapp
 		blk_start_request(orig);
 	else
 		blk_mq_start_request(orig);
-	atomic_inc(&md->pending[rq_data_dir(orig)]);
+	atomic_inc(&dm_disk(md)->part0.in_flight[rq_data_dir(orig)]);
 
 	if (md->seq_rq_merge_deadline_usecs) {
 		md->last_rq_pos = rq_end_sector(orig);