bio-integrity: Fix bio_integrity_verify segment start bug

This patch addresses a bug in bio_integrity_verify() code that has
been causing DIF READ verify operations to be silently skipped.

The issue is that bio->bi_idx will have been incremented within
bio_advance() code in the normal blk_update_request() ->
req_bio_endio() completion path, and bio_integrity_verify() is
using bio_for_each_segment() which starts the bio segment walk
at the current bio->bi_idx.

So instead use bio_for_each_segment_all() to always start the bio
segment walk from zero, regardless of the current bio->bi_idx
value after bio_advance() has been called.

Cc: Martin K. Petersen <martin.petersen@oracle.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
Cc: stable@kernel.dk # >= v3.10
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/bio-integrity.c

@@ -447,20 +447,21 @@ static int bio_integrity_verify(struct bio *bio)
 {
 	struct blk_integrity *bi = bdev_get_integrity(bio->bi_bdev);
 	struct blk_integrity_exchg bix;
-	struct bio_vec bv;
-	struct bvec_iter iter;
+	struct bio_vec *bv;
 	sector_t sector = bio->bi_integrity->bip_iter.bi_sector;
 	unsigned int sectors, total, ret;
 	void *prot_buf = bio->bi_integrity->bip_buf;
+	int i;
 
 	ret = total = 0;
 	bix.disk_name = bio->bi_bdev->bd_disk->disk_name;
 	bix.sector_size = bi->sector_size;
 
-	bio_for_each_segment(bv, bio, iter) {
-		void *kaddr = kmap_atomic(bv.bv_page);
-		bix.data_buf = kaddr + bv.bv_offset;
-		bix.data_size = bv.bv_len;
+	bio_for_each_segment_all(bv, bio, i) {
+		void *kaddr = kmap_atomic(bv->bv_page);
+
+		bix.data_buf = kaddr + bv->bv_offset;
+		bix.data_size = bv->bv_len;
 		bix.prot_buf = prot_buf;
 		bix.sector = sector;
 
@@ -471,7 +472,7 @@ static int bio_integrity_verify(struct bio *bio)
 			return ret;
 		}
 
-		sectors = bv.bv_len / bi->sector_size;
+		sectors = bv->bv_len / bi->sector_size;
 		sector += sectors;
 		prot_buf += sectors * bi->tuple_size;
 		total += sectors * bi->tuple_size;