block, direct-io: fix OOM by converting to bio_for_each_page_all()

There has been an occasional out-of-memory problem with multipage bvecs.

Fix the bug by converting bio_for_each_segment_all() to
bio_for_each_page_all(), both in bio_check_pages_dirty() and
dio_bio_complete().

To reproduce the OOM, run xfstests/generic/113 infinitely:

while [ 1 ] ; do
	./check generic/113
done

TODO: audit other uses of bio_for_each_segment_all()

Signed-off-by: Ming Lin <mlin@minggr.net>
[dpark: add more description into commit message]
Signed-off-by: Dongsu Park <dongsu.park@profitbricks.com>

block/bio.c

@@ -1661,16 +1661,16 @@ static void bio_dirty_fn(struct work_struct *work)
 
 void bio_check_pages_dirty(struct bio *bio)
 {
-	struct bio_vec *bvec;
+	struct bio_vec bvec;
+	struct bvec_iter iter;
 	int nr_clean_pages = 0;
-	int i;
 
-	bio_for_each_segment_all(bvec, bio, i) {
-		struct page *page = bvec->bv_page;
+	bio_for_each_page_all(bvec, bio, iter) {
+		struct page *page = bvec.bv_page;
 
 		if (PageDirty(page) || PageCompound(page)) {
 			page_cache_release(page);
-			bvec->bv_page = NULL;
+			bvec.bv_page = NULL;
 		} else {
 			nr_clean_pages++;
 		}

fs/direct-io.c

@@ -457,17 +457,17 @@ static struct bio *dio_await_one(struct dio *dio)
 static int dio_bio_complete(struct dio *dio, struct bio *bio)
 {
 	const int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
-	struct bio_vec *bvec;
-	unsigned i;
+	struct bio_vec bvec;
+	struct bvec_iter iter;
 
 	if (!uptodate)
 		dio->io_error = -EIO;
 
 	if (dio->is_async && dio->rw == READ) {
 		bio_check_pages_dirty(bio);	/* transfers ownership */
 	} else {
-		bio_for_each_segment_all(bvec, bio, i) {
-			struct page *page = bvec->bv_page;
+		bio_for_each_page_all(bvec, bio, iter) {
+			struct page *page = bvec.bv_page;
 
 			if (dio->rw == READ && !PageCompound(page))
 				set_page_dirty_lock(page);