[PATCH v12 09/10] block: Convert bio_iov_iter_get_pages to use iov_iter_extract_pages

David Howells
2023-02-07T17:16:15Z

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@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
---

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 547e38883934..fc57f0aa098e 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -1212,7 +1212,7 @@ 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;
}

@@ -1226,7 +1226,7 @@ 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;
}

@@ -1237,10 +1237,10 @@ 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)
{
@@ -1272,9 +1272,9 @@ 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;

@@ -1307,7 +1307,7 @@ 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;
}
@@ -1342,7 +1342,8 @@ 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));