On Mon 22-05-23 21:57:43, David Howells wrote:
> 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 affected by/visible to the
> child process).
>
> Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
> Reviewed-by: Christoph Hellwig <hch@xxxxxx>
> Reviewed-by: John Hubbard <jhubbard@xxxxxxxxxx>
> cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
> cc: Jens Axboe <axboe@xxxxxxxxx>
> cc: Jan Kara <jack@xxxxxxx>
> cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> cc: Logan Gunthorpe <logang@xxxxxxxxxxxx>
> cc: linux-block@xxxxxxxxxxxxxxx
> ---
Looks good. Feel free to add:
Reviewed-by: Jan Kara <jack@xxxxxxx>
Honza
>
> Notes:
> ver #10)
> - Drop bio_set_cleanup_mode(), open coding it instead.
>
> ver #8)
> - Split the patch up a bit [hch].
> - We should only be using pinned/non-pinned pages and not ref'd pages,
> so adjust the comments appropriately.
>
> ver #7)
> - Don't treat BIO_PAGE_REFFED/PINNED as being the same as FOLL_GET/PIN.
>
> ver #5)
> - Transcribe the FOLL_* flags returned by iov_iter_extract_pages() to
> BIO_* flags and got rid of bi_cleanup_mode.
> - Replaced BIO_NO_PAGE_REF to BIO_PAGE_REFFED in the preceding patch.
>
> block/bio.c | 23 ++++++++++++-----------
> 1 file changed, 12 insertions(+), 11 deletions(-)
>
> diff --git a/block/bio.c b/block/bio.c
> index 17bd01ecde36..798cc4cf3bd2 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -1205,7 +1205,7 @@ static int bio_iov_add_page(struct bio *bio, struct page *page,
> }
>
> if (same_page)
> - put_page(page);
> + bio_release_page(bio, page);
> return 0;
> }
>
> @@ -1219,7 +1219,7 @@ static int bio_iov_add_zone_append_page(struct bio *bio, struct page *page,
> queue_max_zone_append_sectors(q), &same_page) != len)
> return -EINVAL;
> if (same_page)
> - put_page(page);
> + bio_release_page(bio, page);
> return 0;
> }
>
> @@ -1230,10 +1230,10 @@ static int bio_iov_add_zone_append_page(struct bio *bio, struct page *page,
> * @bio: bio to add pages to
> * @iter: iov iterator describing the region to be mapped
> *
> - * Pins pages from *iter and appends them to @bio's bvec array. The
> - * pages will have to be released using put_page() when done.
> - * For multi-segment *iter, this function only adds pages from the
> - * next non-empty segment of the iov iterator.
> + * Extracts pages from *iter and appends them to @bio's bvec array. The pages
> + * will have to be cleaned up in the way indicated by the BIO_PAGE_PINNED flag.
> + * For a multi-segment *iter, this function only adds pages from the next
> + * non-empty segment of the iov iterator.
> */
> static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
> {
> @@ -1265,9 +1265,9 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
> * result to ensure the bio's total size is correct. The remainder of
> * the iov data will be picked up in the next bio iteration.
> */
> - size = iov_iter_get_pages(iter, pages,
> - UINT_MAX - bio->bi_iter.bi_size,
> - nr_pages, &offset, extraction_flags);
> + size = iov_iter_extract_pages(iter, &pages,
> + UINT_MAX - bio->bi_iter.bi_size,
> + nr_pages, extraction_flags, &offset);
> if (unlikely(size <= 0))
> return size ? size : -EFAULT;
>
> @@ -1300,7 +1300,7 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
> iov_iter_revert(iter, left);
> out:
> while (i < nr_pages)
> - put_page(pages[i++]);
> + bio_release_page(bio, pages[i++]);
>
> return ret;
> }
> @@ -1335,7 +1335,8 @@ int bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
> return 0;
> }
>
> - bio_set_flag(bio, BIO_PAGE_REFFED);
> + if (iov_iter_extract_will_pin(iter))
> + bio_set_flag(bio, BIO_PAGE_PINNED);
> do {
> ret = __bio_iov_iter_get_pages(bio, iter);
> } while (!ret && iov_iter_count(iter) && !bio_full(bio, 0));
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
