Commit 403b6fb8 authored by David Howells's avatar David Howells Committed by Jens Axboe
Browse files

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: default avatarDavid Howells <dhowells@redhat.com>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Reviewed-by: default avatarJohn 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: default avatarJan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20230522205744.2825689-7-dhowells@redhat.com


Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent a7e689dd

block/blk-map.c

+11 −12
Original line number Diff line number Diff line
@@ -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? */