[PATCH] Fix md using bio on stack with bio clones

If md resides on top of a driver using bio_clone() (such as dm), it will
oops the kernel due to md submitting a botched bio that has a veclist but
doesn't have bio->bi_max_vecs set.
Signed-off-by: Jens Axboe <axboe@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

drivers/md/md.c

@@ -332,29 +332,26 @@ static int bi_complete(struct bio *bio, unsigned int bytes_done, int error)
 static int sync_page_io(struct block_device *bdev, sector_t sector, int size,
 		   struct page *page, int rw)
 {
-	struct bio bio;
-	struct bio_vec vec;
+	struct bio *bio = bio_alloc(GFP_KERNEL, 1);
 	struct completion event;
+	int ret;
+
+	bio_get(bio);
 
 	rw |= (1 << BIO_RW_SYNC);
 
-	bio_init(&bio);
-	bio.bi_io_vec = &vec;
-	vec.bv_page = page;
-	vec.bv_len = size;
-	vec.bv_offset = 0;
-	bio.bi_vcnt = 1;
-	bio.bi_idx = 0;
-	bio.bi_size = size;
-	bio.bi_bdev = bdev;
-	bio.bi_sector = sector;
+	bio->bi_bdev = bdev;
+	bio->bi_sector = sector;
+	bio_add_page(bio, page, size, 0);
 	init_completion(&event);
-	bio.bi_private = &event;
-	bio.bi_end_io = bi_complete;
-	submit_bio(rw, &bio);
+	bio->bi_private = &event;
+	bio->bi_end_io = bi_complete;
+	submit_bio(rw, bio);
 	wait_for_completion(&event);
 
-	return test_bit(BIO_UPTODATE, &bio.bi_flags);
+	ret = test_bit(BIO_UPTODATE, &bio->bi_flags);
+	bio_put(bio);
+	return ret;
 }
 
 static int read_disk_sb(mdk_rdev_t * rdev)