Messages in this thread | | | From | KOSAKI Motohiro <> | Subject | Re: [PATCH 2/4] swap: prevent reuse during hibernation | Date | Tue, 7 Sep 2010 10:03:26 +0900 (JST) |
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> 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 > --- > > 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; > +
I like this one. Reviewed-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
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