lightnvm: pblk: fix crash in pblk_end_partial_read due to multipage bvecs

The introduction of multipage bio vectors broke pblk's partial read
logic due to it not being prepared for multipage bio vectors.

Use bio vector iterators instead of direct bio vector indexing.

Fixes: 07173c3ec2 ("block: enable multipage bvecs")
Reported-by: Klaus Jensen <klaus.jensen@cnexlabs.com>
Signed-off-by: Hans Holmberg <hans.holmberg@cnexlabs.com>
Updated description.
Signed-off-by: Matias Bjørling <mb@lightnvm.io>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/lightnvm/pblk-read.c

@@ -231,14 +231,14 @@ static void pblk_end_partial_read(struct nvm_rq *rqd)
 	struct pblk_sec_meta *meta;
 	struct bio *new_bio = rqd->bio;
 	struct bio *bio = pr_ctx->orig_bio;
-	struct bio_vec src_bv, dst_bv;
 	void *meta_list = rqd->meta_list;
-	int bio_init_idx = pr_ctx->bio_init_idx;
 	unsigned long *read_bitmap = pr_ctx->bitmap;
+	struct bvec_iter orig_iter = BVEC_ITER_ALL_INIT;
+	struct bvec_iter new_iter = BVEC_ITER_ALL_INIT;
 	int nr_secs = pr_ctx->orig_nr_secs;
 	int nr_holes = nr_secs - bitmap_weight(read_bitmap, nr_secs);
 	void *src_p, *dst_p;
-	int hole, i;
+	int bit, i;
 
 	if (unlikely(nr_holes == 1)) {
 		struct ppa_addr ppa;
@@ -257,33 +257,39 @@ static void pblk_end_partial_read(struct nvm_rq *rqd)
 
 	/* Fill the holes in the original bio */
 	i = 0;
-	hole = find_first_zero_bit(read_bitmap, nr_secs);
-	do {
-		struct pblk_line *line;
+	for (bit = 0; bit < nr_secs; bit++) {
+		if (!test_bit(bit, read_bitmap)) {
+			struct bio_vec dst_bv, src_bv;
+			struct pblk_line *line;
 
-		line = pblk_ppa_to_line(pblk, rqd->ppa_list[i]);
-		kref_put(&line->ref, pblk_line_put);
+			line = pblk_ppa_to_line(pblk, rqd->ppa_list[i]);
+			kref_put(&line->ref, pblk_line_put);
 
-		meta = pblk_get_meta(pblk, meta_list, hole);
-		meta->lba = cpu_to_le64(pr_ctx->lba_list_media[i]);
+			meta = pblk_get_meta(pblk, meta_list, bit);
+			meta->lba = cpu_to_le64(pr_ctx->lba_list_media[i]);
 
-		src_bv = new_bio->bi_io_vec[i++];
-		dst_bv = bio->bi_io_vec[bio_init_idx + hole];
+			dst_bv = bio_iter_iovec(bio, orig_iter);
+			src_bv = bio_iter_iovec(new_bio, new_iter);
 
-		src_p = kmap_atomic(src_bv.bv_page);
-		dst_p = kmap_atomic(dst_bv.bv_page);
+			src_p = kmap_atomic(src_bv.bv_page);
+			dst_p = kmap_atomic(dst_bv.bv_page);
 
-		memcpy(dst_p + dst_bv.bv_offset,
-			src_p + src_bv.bv_offset,
-			PBLK_EXPOSED_PAGE_SIZE);
+			memcpy(dst_p + dst_bv.bv_offset,
+				src_p + src_bv.bv_offset,
+				PBLK_EXPOSED_PAGE_SIZE);
 
-		kunmap_atomic(src_p);
-		kunmap_atomic(dst_p);
+			kunmap_atomic(src_p);
+			kunmap_atomic(dst_p);
 
-		mempool_free(src_bv.bv_page, &pblk->page_bio_pool);
+			flush_dcache_page(dst_bv.bv_page);
+			mempool_free(src_bv.bv_page, &pblk->page_bio_pool);
 
-		hole = find_next_zero_bit(read_bitmap, nr_secs, hole + 1);
-	} while (hole < nr_secs);
+			bio_advance_iter(new_bio, &new_iter,
+					PBLK_EXPOSED_PAGE_SIZE);
+			i++;
+		}
+		bio_advance_iter(bio, &orig_iter, PBLK_EXPOSED_PAGE_SIZE);
+	}
 
 	bio_put(new_bio);
 	kfree(pr_ctx);