block: convert bio_map_user_iov to use iov_iter_extract_pages

This will pin pages or leave them unaltered rather than getting a ref on
them as appropriate to the iterator.

The pages need to be pinned for DIO rather than having refs taken on them
to prevent VM copy-on-write from malfunctioning during a concurrent fork()
(the result of the I/O could otherwise end up being visible to/affected by
the child process).
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
cc: Al Viro <viro@zeniv.linux.org.uk>
cc: Jens Axboe <axboe@kernel.dk>
cc: Jan Kara <jack@suse.cz>
cc: Matthew Wilcox <willy@infradead.org>
cc: Logan Gunthorpe <logang@deltatee.com>
cc: linux-block@vger.kernel.org
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20230522205744.2825689-7-dhowells@redhat.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-map.c

@@ -281,22 +281,21 @@ static int bio_map_user_iov(struct request *rq, struct iov_iter *iter,
 
 	if (blk_queue_pci_p2pdma(rq->q))
 		extraction_flags |= ITER_ALLOW_P2PDMA;
+	if (iov_iter_extract_will_pin(iter))
+		bio_set_flag(bio, BIO_PAGE_PINNED);
 
-	bio_set_flag(bio, BIO_PAGE_REFFED);
 	while (iov_iter_count(iter)) {
-		struct page **pages, *stack_pages[UIO_FASTIOV];
+		struct page *stack_pages[UIO_FASTIOV];
+		struct page **pages = stack_pages;
 		ssize_t bytes;
 		size_t offs;
 		int npages;
 
-		if (nr_vecs <= ARRAY_SIZE(stack_pages)) {
-			pages = stack_pages;
-			bytes = iov_iter_get_pages(iter, pages, LONG_MAX,
-						   nr_vecs, &offs, extraction_flags);
-		} else {
-			bytes = iov_iter_get_pages_alloc(iter, &pages,
-						LONG_MAX, &offs, extraction_flags);
-		}
+		if (nr_vecs > ARRAY_SIZE(stack_pages))
+			pages = NULL;
+
+		bytes = iov_iter_extract_pages(iter, &pages, LONG_MAX,
+					       nr_vecs, extraction_flags, &offs);
 		if (unlikely(bytes <= 0)) {
 			ret = bytes ? bytes : -EFAULT;
 			goto out_unmap;
@@ -318,7 +317,7 @@ static int bio_map_user_iov(struct request *rq, struct iov_iter *iter,
 				if (!bio_add_hw_page(rq->q, bio, page, n, offs,
 						     max_sectors, &same_page)) {
 					if (same_page)
-						put_page(page);
+						bio_release_page(bio, page);
 					break;
 				}
 
@@ -330,7 +329,7 @@ static int bio_map_user_iov(struct request *rq, struct iov_iter *iter,
 		 * release the pages we didn't map into the bio, if any
 		 */
 		while (j < npages)
-			put_page(pages[j++]);
+			bio_release_page(bio, pages[j++]);
 		if (pages != stack_pages)
 			kvfree(pages);
 		/* couldn't stuff something into bio? */