lightnvm: pblk: fix freeing of merged pages

bio_add_pc_page() may merge pages when a bio is padded due to a flush.
Fix iteration over the bio to free the correct pages in case of a merge.
Signed-off-by: Heiner Litz <hlitz@ucsc.edu>
Reviewed-by: Javier González <javier@javigon.com>
Signed-off-by: Matias Bjørling <mb@lightnvm.io>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/lightnvm/pblk-core.c

@@ -323,14 +323,16 @@ void pblk_free_rqd(struct pblk *pblk, struct nvm_rq *rqd, int type)
 void pblk_bio_free_pages(struct pblk *pblk, struct bio *bio, int off,
 			 int nr_pages)
 {
-	struct bio_vec bv;
-	int i;
-
-	WARN_ON(off + nr_pages != bio->bi_vcnt);
-
-	for (i = off; i < nr_pages + off; i++) {
-		bv = bio->bi_io_vec[i];
-		mempool_free(bv.bv_page, &pblk->page_bio_pool);
+	struct bio_vec *bv;
+	struct page *page;
+	int i, e, nbv = 0;
+
+	for (i = 0; i < bio->bi_vcnt; i++) {
+		bv = &bio->bi_io_vec[i];
+		page = bv->bv_page;
+		for (e = 0; e < bv->bv_len; e += PBLK_EXPOSED_PAGE_SIZE, nbv++)
+			if (nbv >= off)
+				mempool_free(page++, &pblk->page_bio_pool);
 	}
 }