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 <hughd@xxxxxxxxxx>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Cc: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
Cc: "Rafael J. Wysocki" <rjw@xxxxxxx>
Cc: Ondrej Zary <linux@xxxxxxxxxxxxxxxxxxxx>
Cc: Andrea Gelmini <andrea.gelmini@xxxxxxxxx>
Cc: Balbir Singh <balbir@xxxxxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Nigel Cunningham <nigel@xxxxxxxxxxxx>
Cc: stable@xxxxxxxxxx
---
mm/swapfile.c | 24 ++++++++++++++++++++----
1 file changed, 20 insertions(+), 4 deletions(-)
--- swap1/mm/swapfile.c 2010-09-05 22:37:07.000000000 -0700
+++ swap2/mm/swapfile.c 2010-09-05 22:45:54.000000000 -0700
@@ -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;
--
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