Commit 4a93025c authored by David Hildenbrand's avatar David Hildenbrand Committed by Linus Torvalds

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: default avatarDavid Hildenbrand <david@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: default avatarWei Yang <richard.weiyang@linux.alibaba.com>
Acked-by: default avatarMichal Hocko <mhocko@suse.com>
Acked-by: default avatarDan 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.comSigned-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent c1a06df6
...@@ -58,25 +58,25 @@ module_param_call(shuffle, shuffle_store, shuffle_show, &shuffle_param, 0400); ...@@ -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 * 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. * '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 * Given we're dealing with randomly selected pfns in a zone we
* need to ask questions like... * need to ask questions like...
*/ */
/* ...is the pfn even in the memmap? */ /* ... is the page managed by the buddy? */
if (!pfn_valid_within(pfn)) if (!page)
return NULL; return NULL;
/* ...is the pfn in a present section or a hole? */ /* ... is the page assigned to the same zone? */
if (!pfn_in_present_section(pfn)) if (page_zone(page) != zone)
return NULL; return NULL;
/* ...is the page free and currently on a free_area list? */ /* ...is the page free and currently on a free_area list? */
page = pfn_to_page(pfn);
if (!PageBuddy(page)) if (!PageBuddy(page))
return NULL; return NULL;
...@@ -123,7 +123,7 @@ void __meminit __shuffle_zone(struct zone *z) ...@@ -123,7 +123,7 @@ void __meminit __shuffle_zone(struct zone *z)
* page_j randomly selected in the span @zone_start_pfn to * page_j randomly selected in the span @zone_start_pfn to
* @spanned_pages. * @spanned_pages.
*/ */
page_i = shuffle_valid_page(i, order); page_i = shuffle_valid_page(z, i, order);
if (!page_i) if (!page_i)
continue; continue;
...@@ -137,7 +137,7 @@ void __meminit __shuffle_zone(struct zone *z) ...@@ -137,7 +137,7 @@ void __meminit __shuffle_zone(struct zone *z)
j = z->zone_start_pfn + j = z->zone_start_pfn +
ALIGN_DOWN(get_random_long() % z->spanned_pages, ALIGN_DOWN(get_random_long() % z->spanned_pages,
order_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) if (page_j && page_j != page_i)
break; break;
} }
......
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