On Mon 22-05-23 21:57:44, 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 visible to/affected by
> 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/blk-map.c | 23 +++++++++++------------
> 1 file changed, 11 insertions(+), 12 deletions(-)
>
> diff --git a/block/blk-map.c b/block/blk-map.c
> index 33d9f6e89ba6..3551c3ff17cf 100644
> --- a/block/blk-map.c
> +++ b/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? */
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
