From a26ee565b6cd8dc2bf15ff6aa70bbb28f928b773 Mon Sep 17 00:00:00 2001 From: Qian Cai Date: Fri, 18 Oct 2019 20:19:29 -0700 Subject: [PATCH] mm/page_owner: don't access uninitialized memmaps when reading /proc/pagetypeinfo Uninitialized memmaps contain garbage and in the worst case trigger kernel BUGs, especially with CONFIG_PAGE_POISONING. They should not get touched. For example, when not onlining a memory block that is spanned by a zone and reading /proc/pagetypeinfo with CONFIG_DEBUG_VM_PGFLAGS and CONFIG_PAGE_POISONING, we can trigger a kernel BUG: :/# echo 1 > /sys/devices/system/memory/memory40/online :/# echo 1 > /sys/devices/system/memory/memory42/online :/# cat /proc/pagetypeinfo > test.file page:fffff2c585200000 is uninitialized and poisoned raw: ffffffffffffffff ffffffffffffffff ffffffffffffffff ffffffffffffffff raw: ffffffffffffffff ffffffffffffffff ffffffffffffffff ffffffffffffffff page dumped because: VM_BUG_ON_PAGE(PagePoisoned(p)) There is not page extension available. ------------[ cut here ]------------ kernel BUG at include/linux/mm.h:1107! invalid opcode: 0000 [#1] SMP NOPTI Please note that this change does not affect ZONE_DEVICE, because pagetypeinfo_showmixedcount_print() is called from mm/vmstat.c:pagetypeinfo_showmixedcount() only for populated zones, and ZONE_DEVICE is never populated (zone->present_pages always 0). [david@redhat.com: move check to outer loop, add comment, rephrase description] Link: http://lkml.kernel.org/r/20191011140638.8160-1-david@redhat.com Fixes: f1dd2cd13c4b ("mm, memory_hotplug: do not associate hotadded memory to zones until online") # visible after d0dc12e86b319 Signed-off-by: Qian Cai Signed-off-by: David Hildenbrand Acked-by: Michal Hocko Acked-by: Vlastimil Babka Cc: Thomas Gleixner Cc: "Peter Zijlstra (Intel)" Cc: Miles Chen Cc: Mike Rapoport Cc: Qian Cai Cc: Greg Kroah-Hartman Cc: [4.13+] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/page_owner.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/mm/page_owner.c b/mm/page_owner.c index e327bcd..18ecde9 100644 --- a/mm/page_owner.c +++ b/mm/page_owner.c @@ -271,7 +271,8 @@ void pagetypeinfo_showmixedcount_print(struct seq_file *m, * not matter as the mixed block count will still be correct */ for (; pfn < end_pfn; ) { - if (!pfn_valid(pfn)) { + page = pfn_to_online_page(pfn); + if (!page) { pfn = ALIGN(pfn + 1, MAX_ORDER_NR_PAGES); continue; } @@ -279,13 +280,13 @@ void pagetypeinfo_showmixedcount_print(struct seq_file *m, block_end_pfn = ALIGN(pfn + 1, pageblock_nr_pages); block_end_pfn = min(block_end_pfn, end_pfn); - page = pfn_to_page(pfn); pageblock_mt = get_pageblock_migratetype(page); for (; pfn < block_end_pfn; pfn++) { if (!pfn_valid_within(pfn)) continue; + /* The pageblock is online, no need to recheck. */ page = pfn_to_page(pfn); if (page_zone(page) != zone) -- 2.7.4