dm mpath: fix missing call of path selector type->end_io

After commit 396eaf2 ("blk-mq: improve DM's blk-mq IO merging via
blk_insert_cloned_request feedback"), map_request() will requeue the tio
when issued clone request return BLK_STS_RESOURCE or BLK_STS_DEV_RESOURCE.

Thus, if device driver status is error, a tio may be requeued multiple
times until the return value is not DM_MAPIO_REQUEUE.  That means
type->start_io may be called multiple times, while type->end_io is only
called when IO complete.

In fact, even without commit 396eaf2, setup_clone() failure can
also cause tio requeue and associated missed call to type->end_io.

The service-time path selector selects path based on in_flight_size,
which is increased by st_start_io() and decreased by st_end_io().
Missed calls to st_end_io() can lead to in_flight_size count error and
will cause the selector to make the wrong choice.  In addition,
queue-length path selector will also be affected.

To fix the problem, call type->end_io in ->release_clone_rq before tio
requeue.  map_info is passed to ->release_clone_rq() for map_request()
error path that result in requeue.

Fixes: 396eaf2 ("blk-mq: improve DM's blk-mq IO merging via blk_insert_cloned_request feedback")
Cc: stable@vger.kernl.org
Signed-off-by: Yufen Yu <yuyufen@huawei.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm-mpath.c

@@ -544,8 +544,23 @@ static int multipath_clone_and_map(struct dm_target *ti, struct request *rq,
 	return DM_MAPIO_REMAPPED;
 }
 
-static void multipath_release_clone(struct request *clone)
+static void multipath_release_clone(struct request *clone,
+				    union map_info *map_context)
 {
+	if (unlikely(map_context)) {
+		/*
+		 * non-NULL map_context means caller is still map
+		 * method; must undo multipath_clone_and_map()
+		 */
+		struct dm_mpath_io *mpio = get_mpio(map_context);
+		struct pgpath *pgpath = mpio->pgpath;
+
+		if (pgpath && pgpath->pg->ps.type->end_io)
+			pgpath->pg->ps.type->end_io(&pgpath->pg->ps,
+						    &pgpath->path,
+						    mpio->nr_bytes);
+	}
+
 	blk_put_request(clone);
 }
 

drivers/md/dm-rq.c

@@ -168,7 +168,7 @@ static void dm_end_request(struct request *clone, blk_status_t error)
 	struct request *rq = tio->orig;
 
 	blk_rq_unprep_clone(clone);
-	tio->ti->type->release_clone_rq(clone);
+	tio->ti->type->release_clone_rq(clone, NULL);
 
 	rq_end_stats(md, rq);
 	blk_mq_end_request(rq, error);
@@ -201,7 +201,7 @@ static void dm_requeue_original_request(struct dm_rq_target_io *tio, bool delay_
 	rq_end_stats(md, rq);
 	if (tio->clone) {
 		blk_rq_unprep_clone(tio->clone);
-		tio->ti->type->release_clone_rq(tio->clone);
+		tio->ti->type->release_clone_rq(tio->clone, NULL);
 	}
 
 	dm_mq_delay_requeue_request(rq, delay_ms);
@@ -398,7 +398,7 @@ static int map_request(struct dm_rq_target_io *tio)
 	case DM_MAPIO_REMAPPED:
 		if (setup_clone(clone, rq, tio, GFP_ATOMIC)) {
 			/* -ENOMEM */
-			ti->type->release_clone_rq(clone);
+			ti->type->release_clone_rq(clone, &tio->info);
 			return DM_MAPIO_REQUEUE;
 		}
 
@@ -408,7 +408,7 @@ static int map_request(struct dm_rq_target_io *tio)
 		ret = dm_dispatch_clone_request(clone, rq);
 		if (ret == BLK_STS_RESOURCE || ret == BLK_STS_DEV_RESOURCE) {
 			blk_rq_unprep_clone(clone);
-			tio->ti->type->release_clone_rq(clone);
+			tio->ti->type->release_clone_rq(clone, &tio->info);
 			tio->clone = NULL;
 			return DM_MAPIO_REQUEUE;
 		}

drivers/md/dm-target.c

@@ -136,7 +136,8 @@ static int io_err_clone_and_map_rq(struct dm_target *ti, struct request *rq,
 	return DM_MAPIO_KILL;
 }
 
-static void io_err_release_clone_rq(struct request *clone)
+static void io_err_release_clone_rq(struct request *clone,
+				    union map_info *map_context)
 {
 }
 

include/linux/device-mapper.h

@@ -62,7 +62,8 @@ typedef int (*dm_clone_and_map_request_fn) (struct dm_target *ti,
 					    struct request *rq,
 					    union map_info *map_context,
 					    struct request **clone);
-typedef void (*dm_release_clone_request_fn) (struct request *clone);
+typedef void (*dm_release_clone_request_fn) (struct request *clone,
+					     union map_info *map_context);
 
 /*
  * Returns: