From: Qian Cai <cai@xxxxxx> 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 [ 42.489856] page:fffff2c585200000 is uninitialized and poisoned [ 42.489861] raw: ffffffffffffffff ffffffffffffffff ffffffffffffffff ffffffffffffffff [ 42.492235] raw: ffffffffffffffff ffffffffffffffff ffffffffffffffff ffffffffffffffff [ 42.493501] page dumped because: VM_BUG_ON_PAGE(PagePoisoned(p)) [ 42.494533] There is not page extension available. [ 42.495358] ------------[ cut here ]------------ [ 42.496163] kernel BUG at include/linux/mm.h:1107! [ 42.497069] invalid opcode: 0000 [#1] SMP NOPTI Please not 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). Fixes: f1dd2cd13c4b ("mm, memory_hotplug: do not associate hotadded memory to zones until online") # visible after d0dc12e86b319 Signed-off-by: Qian Cai <cai@xxxxxx> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Cc: Vlastimil Babka <vbabka@xxxxxxx> Cc: Michal Hocko <mhocko@xxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: "Peter Zijlstra (Intel)" <peterz@xxxxxxxxxxxxx> Cc: Miles Chen <miles.chen@xxxxxxxxxxxx> Cc: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx> Cc: Qian Cai <cai@xxxxxx> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> [ move check to outer loop, add comment, rephrase description ] Signed-off-by: David Hildenbrand <david@xxxxxxxxxx> --- Cai asked me to follow up on: [PATCH] mm/page_owner: fix a crash after memory offline --- 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 dee931184788..7d149211f6be 100644 --- a/mm/page_owner.c +++ b/mm/page_owner.c @@ -284,7 +284,8 @@ 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; } @@ -292,13 +293,13 @@ 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) -- 2.21.0