dm: ignore discard return value

__blkdev_issue_discard() always returns 0, making all error checking
at call sites dead code.

For dm-thin change issue_discard() return type to void, in
passdown_double_checking_shared_status() remove the r assignment from
return value of the issue_discard(), for end_discard() hardcode value of
r to 0 that matches only value returned from __blkdev_issue_discard().

Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Chaitanya Kulkarni <ckulkarnilinux@gmail.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>

Author: ChaitanayaKulkarni

drivers/md/dm-thin.c

@@ -395,13 +395,13 @@ static void begin_discard(struct discard_op *op, struct thin_c *tc, struct bio *
 	op->bio = NULL;
 }
 
-static int issue_discard(struct discard_op *op, dm_block_t data_b, dm_block_t data_e)
+static void issue_discard(struct discard_op *op, dm_block_t data_b, dm_block_t data_e)
 {
 	struct thin_c *tc = op->tc;
 	sector_t s = block_to_sectors(tc->pool, data_b);
 	sector_t len = block_to_sectors(tc->pool, data_e - data_b);
 
-	return __blkdev_issue_discard(tc->pool_dev->bdev, s, len, GFP_NOIO, &op->bio);
+	__blkdev_issue_discard(tc->pool_dev->bdev, s, len, GFP_NOIO, &op->bio);
 }
 
 static void end_discard(struct discard_op *op, int r)
@@ -1113,9 +1113,7 @@ static void passdown_double_checking_shared_status(struct dm_thin_new_mapping *m
 				break;
 		}
 
-		r = issue_discard(&op, b, e);
-		if (r)
-			goto out;
+		issue_discard(&op, b, e);
 
 		b = e;
 	}
@@ -1188,8 +1186,8 @@ static void process_prepared_discard_passdown_pt1(struct dm_thin_new_mapping *m)
 		struct discard_op op;
 
 		begin_discard(&op, tc, discard_parent);
-		r = issue_discard(&op, m->data_block, data_end);
-		end_discard(&op, r);
+		issue_discard(&op, m->data_block, data_end);
+		end_discard(&op, 0);
 	}
 }