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Commit b73d7fce authored by Hugh Dickins's avatar Hugh Dickins Committed by Linus Torvalds
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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: default avatarHugh 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 910321ea

mm/swapfile.c

+20 −4
Original line number Diff line number Diff line
@@ -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;