Commit 8ea2979c authored by Matthew Wilcox (Oracle)'s avatar Matthew Wilcox (Oracle)
Browse files

mm/gup: Increment the page refcount before the pincount 



We should always increase the refcount before doing anything else to
the page so that other page users see the elevated refcount first.

Signed-off-by: default avatarMatthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: default avatarJohn Hubbard <jhubbard@nvidia.com>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
parent d90a25f8

mm/gup.c

+6 −8
Original line number Diff line number Diff line
@@ -213,25 +213,23 @@ bool __must_check try_grab_page(struct page *page, unsigned int flags) 
	if (flags & FOLL_GET)

		return try_get_page(page);

	else if (flags & FOLL_PIN) {

		int refs = 1;



		page = compound_head(page);



		if (WARN_ON_ONCE(page_ref_count(page) <= 0))

			return false;



		if (hpage_pincount_available(page))

			hpage_pincount_add(page, 1);

		else

			refs = GUP_PIN_COUNTING_BIAS;



		/*

		 * Similar to try_grab_compound_head(): even if using the

		 * hpage_pincount_add/_sub() routines, be sure to

		 * *also* increment the normal page refcount field at least

		 * once, so that the page really is pinned.

		 */

		page_ref_add(page, refs);

		if (hpage_pincount_available(page)) {

			page_ref_add(page, 1);

			hpage_pincount_add(page, 1);

		} else {

			page_ref_add(page, GUP_PIN_COUNTING_BIAS);

		}



		mod_node_page_state(page_pgdat(page), NR_FOLL_PIN_ACQUIRED, 1);

	}