block: makes bio_split support bio without data

discard bio hasn't data attached. We hit a BUG_ON with such bio. This makes
bio_split works for such bio.

Signed-off-by: Shaohua Li <shli@fusionio.com>
Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 14 insertions, 12 deletions

diff --git a/fs/bio.c b/fs/bio.c
index f855e0e1869c..9298c65ad9c7 100644
--- a/fs/bio.c
+++ b/fs/bio.c
@@ -1475,7 +1475,7 @@ struct bio_pair *bio_split(struct bio *bi, int first_sectors)
         trace_block_split(bdev_get_queue(bi->bi_bdev), bi,
                                 bi->bi_sector + first_sectors);
 
-        BUG_ON(bi->bi_vcnt != 1);
+        BUG_ON(bi->bi_vcnt != 1 && bi->bi_vcnt != 0);
         BUG_ON(bi->bi_idx != 0);
         atomic_set(&bp->cnt, 3);
         bp->error = 0;
@@ -1485,20 +1485,22 @@ struct bio_pair *bio_split(struct bio *bi, int first_sectors)
         bp->bio2.bi_size -= first_sectors << 9;
         bp->bio1.bi_size = first_sectors << 9;
 
-        bp->bv1 = bi->bi_io_vec[0];
-        bp->bv2 = bi->bi_io_vec[0];
+        if (bi->bi_vcnt != 0) {
+                bp->bv1 = bi->bi_io_vec[0];
+                bp->bv2 = bi->bi_io_vec[0];
 
-        if (bio_is_rw(bi)) {
-                bp->bv2.bv_offset += first_sectors << 9;
-                bp->bv2.bv_len -= first_sectors << 9;
-                bp->bv1.bv_len = first_sectors << 9;
-        }
+                if (bio_is_rw(bi)) {
+                        bp->bv2.bv_offset += first_sectors << 9;
+                        bp->bv2.bv_len -= first_sectors << 9;
+                        bp->bv1.bv_len = first_sectors << 9;
+                }
 
-        bp->bio1.bi_io_vec = &bp->bv1;
-        bp->bio2.bi_io_vec = &bp->bv2;
+                bp->bio1.bi_io_vec = &bp->bv1;
+                bp->bio2.bi_io_vec = &bp->bv2;
 
-        bp->bio1.bi_max_vecs = 1;
-        bp->bio2.bi_max_vecs = 1;
+                bp->bio1.bi_max_vecs = 1;
+                bp->bio2.bi_max_vecs = 1;
+        }
 
         bp->bio1.bi_end_io = bio_pair_end_1;
         bp->bio2.bi_end_io = bio_pair_end_2;