bcache: Correctly check against BIO_MAX_PAGES

bch_bio_max_sectors() was checking against BIO_MAX_PAGES as if the limit
was for the total bytes in the bio, not the number of segments.

Signed-off-by: Kent Overstreet <koverstreet@google.com>

drivers/md/bcache/io.c

@@ -158,8 +158,10 @@ static unsigned bch_bio_max_sectors(struct bio *bio)
 {
 	unsigned ret = bio_sectors(bio);
 	struct request_queue *q = bdev_get_queue(bio->bi_bdev);
+	unsigned max_segments = min_t(unsigned, BIO_MAX_PAGES,
+				      queue_max_segments(q));
 	struct bio_vec *bv, *end = bio_iovec(bio) +
-		min_t(int, bio_segments(bio), queue_max_segments(q));
+		min_t(int, bio_segments(bio), max_segments);
 
 	struct bvec_merge_data bvm = {
 		.bi_bdev	= bio->bi_bdev,
@@ -171,7 +173,7 @@ static unsigned bch_bio_max_sectors(struct bio *bio)
 	if (bio->bi_rw & REQ_DISCARD)
 		return min(ret, q->limits.max_discard_sectors);
 
-	if (bio_segments(bio) > queue_max_segments(q) ||
+	if (bio_segments(bio) > max_segments ||
 	    q->merge_bvec_fn) {
 		ret = 0;
 
@@ -183,9 +185,6 @@ static unsigned bch_bio_max_sectors(struct bio *bio)
 			ret		+= bv->bv_len >> 9;
 			bvm.bi_size	+= bv->bv_len;
 		}
-
-		if (ret >= (BIO_MAX_PAGES * PAGE_SIZE) >> 9)
-			return (BIO_MAX_PAGES * PAGE_SIZE) >> 9;
 	}
 
 	ret = min(ret, queue_max_sectors(q));