swap: prevent reuse during hibernation (b73d7fce) · Commits · 戴 / test

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>

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;

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