On Fri 11-10-19 16:06:38, David Hildenbrand wrote:
> 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>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Thanks!
> ---
>
> 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
>
--
Michal Hocko
SUSE Labs
