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: Nick Piggin <npiggin@suse.de>
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/swap_state.c b/mm/swap_state.c
index 67daecb..b526356 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -74,6 +74,7 @@
{
int error;
+ BUG_ON(!PageLocked(page));
BUG_ON(PageSwapCache(page));
BUG_ON(PagePrivate(page));
error = radix_tree_preload(gfp_mask);
@@ -83,7 +84,6 @@
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 @@
{
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);