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Commit b55ed816 authored by Nick Piggin's avatar Nick Piggin Committed by Linus Torvalds
Browse files

mm: clarify __add_to_swap_cache locking 



__add_to_swap_cache unconditionally sets the page locked, which can be a bit
alarming to the unsuspecting reader: in the code paths where the page is
visible to other CPUs, the page should be (and is) already locked.

Instead, just add a check to ensure the page is locked here, and teach the one
path relying on the old behaviour to call SetPageLocked itself.

[hugh@veritas.com: locking fix]
Signed-off-by: default avatarNick Piggin <npiggin@suse.de>
Signed-off-by: default avatarHugh Dickins <hugh@veritas.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 45726cb4

mm/swap_state.c

+4 −1
Original line number Diff line number Diff line
@@ -74,6 +74,7 @@ static int __add_to_swap_cache(struct page *page, swp_entry_t entry, 
{

	int error;



	BUG_ON(!PageLocked(page));

	BUG_ON(PageSwapCache(page));

	BUG_ON(PagePrivate(page));

	error = radix_tree_preload(gfp_mask);
@@ -83,7 +84,6 @@ static int __add_to_swap_cache(struct page *page, swp_entry_t entry, 
						entry.val, page);

		if (!error) {

			page_cache_get(page);

			SetPageLocked(page);

			SetPageSwapCache(page);

			set_page_private(page, entry.val);

			total_swapcache_pages++;
@@ -99,15 +99,18 @@ static int add_to_swap_cache(struct page *page, swp_entry_t entry) 
{

	int error;



	BUG_ON(PageLocked(page));

	if (!swap_duplicate(entry)) {

		INC_CACHE_INFO(noent_race);

		return -ENOENT;

	}

	SetPageLocked(page);

	error = __add_to_swap_cache(page, entry, GFP_KERNEL);

	/*

	 * Anon pages are already on the LRU, we don't run lru_cache_add here.

	 */

	if (error) {

		ClearPageLocked(page);

		swap_free(entry);

		if (error == -EEXIST)

			INC_CACHE_INFO(exist_race);