Commit 4a93025c authored Aug 06, 2020 by David Hildenbrand Committed by Linus Torvalds Aug 07, 2020

mm/shuffle: don't move pages between zones and don't read garbage memmaps



Especially with memory hotplug, we can have offline sections (with a
garbage memmap) and overlapping zones.  We have to make sure to only touch
initialized memmaps (online sections managed by the buddy) and that the
zone matches, to not move pages between zones.

To test if this can actually happen, I added a simple

	BUG_ON(page_zone(page_i) != page_zone(page_j));

right before the swap.  When hotplugging a 256M DIMM to a 4G x86-64 VM and
onlining the first memory block "online_movable" and the second memory
block "online_kernel", it will trigger the BUG, as both zones (NORMAL and
MOVABLE) overlap.

This might result in all kinds of weird situations (e.g., double
allocations, list corruptions, unmovable allocations ending up in the
movable zone).

Fixes: e900a918 ("mm: shuffle initial free memory to improve memory-side-cache utilization")
Signed-off-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Wei Yang <richard.weiyang@linux.alibaba.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Acked-by: Dan Williams <dan.j.williams@intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Huang Ying <ying.huang@intel.com>
Cc: Wei Yang <richard.weiyang@gmail.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: <stable@vger.kernel.org>	[5.2+]
Link: http://lkml.kernel.org/r/20200624094741.9918-2-david@redhat.com


Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent c1a06df6

mm/shuffle.c

+9 −9

Original line number	Diff line number	Diff line
		@@ -58,25 +58,25 @@ module_param_call(shuffle, shuffle_store, shuffle_show, &shuffle_param, 0400);
		* For two pages to be swapped in the shuffle, they must be free (on a
		* 'free_area' lru), have the same order, and have the same migratetype.
		*/
		static struct page * __meminit shuffle_valid_page(unsigned long pfn, int order)
		static struct page * __meminit shuffle_valid_page(struct zone *zone,
		unsigned long pfn, int order)
		{
		struct page *page;
		struct page *page = pfn_to_online_page(pfn);

		/*
		* Given we're dealing with randomly selected pfns in a zone we
		* need to ask questions like...
		*/

		/* ...is the pfn even in the memmap? */
		if (!pfn_valid_within(pfn))
		/* ... is the page managed by the buddy? */
		if (!page)
		return NULL;

		/* ...is the pfn in a present section or a hole? */
		if (!pfn_in_present_section(pfn))
		/* ... is the page assigned to the same zone? */
		if (page_zone(page) != zone)
		return NULL;

		/* ...is the page free and currently on a free_area list? */
		page = pfn_to_page(pfn);
		if (!PageBuddy(page))
		return NULL;

		@@ -123,7 +123,7 @@ void __meminit __shuffle_zone(struct zone *z)
		* page_j randomly selected in the span @zone_start_pfn to
		* @spanned_pages.
		*/
		page_i = shuffle_valid_page(i, order);
		page_i = shuffle_valid_page(z, i, order);
		if (!page_i)
		continue;

		@@ -137,7 +137,7 @@ void __meminit __shuffle_zone(struct zone *z)
		j = z->zone_start_pfn +
		ALIGN_DOWN(get_random_long() % z->spanned_pages,
		order_pages);
		page_j = shuffle_valid_page(j, order);
		page_j = shuffle_valid_page(z, j, order);
		if (page_j && page_j != page_i)
		break;
		}

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