dm: fix __send_changing_extent_only() to send first bio and chain remainder

__send_changing_extent_only() must follow the same pattern that was
established with commit "dm: ensure bio submission follows a depth-first
tree walk".  That is: submit first bio up to split boundary and then
split the remainder to further submissions.
Suggested-by: Mikulas Patocka <mpatocka@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

drivers/md/dm.c

@@ -1348,19 +1348,13 @@ static bool is_split_required_for_discard(struct dm_target *ti)
 	return ti->split_discard_bios;
 }
 
-static int __send_changing_extent_only(struct clone_info *ci,
+static int __send_changing_extent_only(struct clone_info *ci, struct dm_target *ti,
 				       get_num_bios_fn get_num_bios,
 				       is_split_required_fn is_split_required)
 {
-	struct dm_target *ti;
 	unsigned len;
 	unsigned num_bios;
 
-	do {
-		ti = dm_table_find_target(ci->map, ci->sector);
-		if (!dm_target_is_valid(ti))
-			return -EIO;
-
 	/*
 	 * Even though the device advertised support for this type of
 	 * request, that does not mean every target supports it, and
@@ -1379,25 +1373,25 @@ static int __send_changing_extent_only(struct clone_info *ci,
 	__send_duplicate_bios(ci, ti, num_bios, &len);
 
 	ci->sector += len;
-	} while (ci->sector_count -= len);
+	ci->sector_count -= len;
 
 	return 0;
 }
 
-static int __send_discard(struct clone_info *ci)
+static int __send_discard(struct clone_info *ci, struct dm_target *ti)
 {
-	return __send_changing_extent_only(ci, get_num_discard_bios,
+	return __send_changing_extent_only(ci, ti, get_num_discard_bios,
 					   is_split_required_for_discard);
 }
 
-static int __send_write_same(struct clone_info *ci)
+static int __send_write_same(struct clone_info *ci, struct dm_target *ti)
 {
-	return __send_changing_extent_only(ci, get_num_write_same_bios, NULL);
+	return __send_changing_extent_only(ci, ti, get_num_write_same_bios, NULL);
 }
 
-static int __send_write_zeroes(struct clone_info *ci)
+static int __send_write_zeroes(struct clone_info *ci, struct dm_target *ti)
 {
-	return __send_changing_extent_only(ci, get_num_write_zeroes_bios, NULL);
+	return __send_changing_extent_only(ci, ti, get_num_write_zeroes_bios, NULL);
 }
 
 /*
@@ -1410,17 +1404,17 @@ static int __split_and_process_non_flush(struct clone_info *ci)
 	unsigned len;
 	int r;
 
-	if (unlikely(bio_op(bio) == REQ_OP_DISCARD))
-		return __send_discard(ci);
-	else if (unlikely(bio_op(bio) == REQ_OP_WRITE_SAME))
-		return __send_write_same(ci);
-	else if (unlikely(bio_op(bio) == REQ_OP_WRITE_ZEROES))
-		return __send_write_zeroes(ci);
-
 	ti = dm_table_find_target(ci->map, ci->sector);
 	if (!dm_target_is_valid(ti))
 		return -EIO;
 
+	if (unlikely(bio_op(bio) == REQ_OP_DISCARD))
+		return __send_discard(ci, ti);
+	else if (unlikely(bio_op(bio) == REQ_OP_WRITE_SAME))
+		return __send_write_same(ci, ti);
+	else if (unlikely(bio_op(bio) == REQ_OP_WRITE_ZEROES))
+		return __send_write_zeroes(ci, ti);
+
 	if (bio_op(bio) == REQ_OP_ZONE_REPORT)
 		len = ci->sector_count;
 	else