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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 <hughd@google.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
Cc: Ondrej Zary <linux@rainbow-software.org>
Cc: Andrea Gelmini <andrea.gelmini@gmail.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Nigel Cunningham <nigel@tuxonice.net>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Hugh Dickins 2010-09-09 16:38:09 -07:00 committed by Linus Torvalds
parent 910321ea81
commit b73d7fcecd
1 changed files with 20 additions and 4 deletions
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24
mm/swapfile.c
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@ -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;