block: Convert bio_iov_iter_get_pages 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 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
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20230522205744.2825689-6-dhowells@redhat.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/bio.c b/block/bio.c
index 17bd01e..798cc4c 100644 (file)
--- 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));