From b73d7fcecd93dc15eaa3c45c8c587b613f6673c4 Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Thu, 9 Sep 2010 16:38:09 -0700 Subject: [PATCH] swap: prevent reuse during hibernation Move the hibernation check from scan_swap_map() into try_to_free_swap(): to catch not only the common case when hibernation's allocation itself triggers swap reuse, but also the less likely case when concurrent page reclaim (shrink_page_list) might happen to try_to_free_swap from a page. Hibernation already clears __GFP_IO from the gfp_allowed_mask, to stop reclaim from going to swap: check that to prevent swap reuse too. Signed-off-by: Hugh Dickins Cc: KAMEZAWA Hiroyuki Cc: KOSAKI Motohiro Cc: "Rafael J. Wysocki" Cc: Ondrej Zary Cc: Andrea Gelmini Cc: Balbir Singh Cc: Andrea Arcangeli Cc: Nigel Cunningham Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/swapfile.c | 24 ++++++++++++++++++++---- 1 file changed, 20 insertions(+), 4 deletions(-) diff --git a/mm/swapfile.c b/mm/swapfile.c index f08d165871b..ed5151079f5 100644 --- a/mm/swapfile.c +++ b/mm/swapfile.c @@ -318,10 +318,8 @@ checks: if (offset > si->highest_bit) scan_base = offset = si->lowest_bit; - /* reuse swap entry of cache-only swap if not hibernation. */ - if (vm_swap_full() - && usage == SWAP_HAS_CACHE - && si->swap_map[offset] == SWAP_HAS_CACHE) { + /* reuse swap entry of cache-only swap if not busy. */ + if (vm_swap_full() && si->swap_map[offset] == SWAP_HAS_CACHE) { int swap_was_freed; spin_unlock(&swap_lock); swap_was_freed = __try_to_reclaim_swap(si, offset); @@ -688,6 +686,24 @@ int try_to_free_swap(struct page *page) if (page_swapcount(page)) return 0; + /* + * Once hibernation has begun to create its image of memory, + * there's a danger that one of the calls to try_to_free_swap() + * - most probably a call from __try_to_reclaim_swap() while + * hibernation is allocating its own swap pages for the image, + * but conceivably even a call from memory reclaim - will free + * the swap from a page which has already been recorded in the + * image as a clean swapcache page, and then reuse its swap for + * another page of the image. On waking from hibernation, the + * original page might be freed under memory pressure, then + * later read back in from swap, now with the wrong data. + * + * Hibernation clears bits from gfp_allowed_mask to prevent + * memory reclaim from writing to disk, so check that here. + */ + if (!(gfp_allowed_mask & __GFP_IO)) + return 0; + delete_from_swap_cache(page); SetPageDirty(page); return 1; -- 2.39.3