From: Nick Piggin Date: Tue, 16 Oct 2007 08:24:42 +0000 (-0700) Subject: mm: clarify __add_to_swap_cache locking X-Git-Tag: v2.6.24-rc1~1223 X-Git-Url: https://err.no/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=b55ed816235cf41c29159d22a4cdeec7deb5821c;p=linux-2.6 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 Signed-off-by: Hugh Dickins Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/mm/swap_state.c b/mm/swap_state.c index 67daecb603..b52635601d 100644 --- a/mm/swap_state.c +++ b/mm/swap_state.c @@ -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);