Re: [PATCH v3] mm/page_owner: fix for deferred struct page init

[Qian Cai]

On 1/3/19 6:51 AM, Michal Hocko wrote:
> On Thu 20-12-18 15:31:56, Qian Cai wrote:
>> When booting a system with "page_owner=on",
>>
>> start_kernel
>>   page_ext_init
>>     invoke_init_callbacks
>>       init_section_page_ext
>>         init_page_owner
>>           init_early_allocated_pages
>>             init_zones_in_node
>>               init_pages_in_zone
>>                 lookup_page_ext
>>                   page_to_nid
>>
>> The issue here is that page_to_nid() will not work since some page
>> flags have no node information until later in page_alloc_init_late() due
>> to DEFERRED_STRUCT_PAGE_INIT. Hence, it could trigger an out-of-bounds
>> access with an invalid nid.
>>
>> [    8.666047] UBSAN: Undefined behaviour in ./include/linux/mm.h:1104:50
>> [    8.672603] index 7 is out of range for type 'zone [5]'
>>
>> Also, kernel will panic since flags were poisoned earlier with,
>>
>> CONFIG_DEBUG_VM_PGFLAGS=y
>> CONFIG_NODE_NOT_IN_PAGE_FLAGS=n
>>
>> start_kernel
>>   setup_arch
>>     pagetable_init
>>       paging_init
>>         sparse_init
>>           sparse_init_nid
>>             memblock_alloc_try_nid_raw
>>
>> Although later it tries to set page flags for pages in reserved bootmem
>> regions,
>>
>> mm_init
>>   mem_init
>>     memblock_free_all
>>       free_low_memory_core_early
>>         reserve_bootmem_region
>>
>> there could still have some freed pages from the page allocator but yet
>> to be initialized due to DEFERRED_STRUCT_PAGE_INIT. It have already been
>> dealt with a bit in page_ext_init().
>>
>> * Take into account DEFERRED_STRUCT_PAGE_INIT.
>> */
>> if (early_pfn_to_nid(pfn) != nid)
>> 	continue;
>>
>> However, it did not handle it well in init_pages_in_zone() which end up
>> calling page_to_nid().
>>
>> [   11.917212] page:ffffea0004200000 is uninitialized and poisoned
>> [   11.917220] raw: ffffffffffffffff ffffffffffffffff ffffffffffffffff
>> ffffffffffffffff
>> [   11.921745] raw: ffffffffffffffff ffffffffffffffff ffffffffffffffff
>> ffffffffffffffff
>> [   11.924523] page dumped because: VM_BUG_ON_PAGE(PagePoisoned(p))
>> [   11.926498] page_owner info is not active (free page?)
>> [   12.329560] kernel BUG at include/linux/mm.h:990!
>> [   12.337632] RIP: 0010:init_page_owner+0x486/0x520
>>
>> Since there is no other routines depend on page_ext_init() in
>> start_kernel(), just move it after page_alloc_init_late() to ensure that
>> there is no deferred pages need to de dealt with. If deselected
>> DEFERRED_STRUCT_PAGE_INIT, it is still better to call page_ext_init()
>> earlier, so page owner could catch more early page allocation call
>> sites. This gives us a good compromise between catching good and bad
>> call sites (See the v1 patch [1]) in case of DEFERRED_STRUCT_PAGE_INIT.
>>
>> [1] https://lore.kernel.org/lkml/20181220060303.38686-1-cai@xxxxxx/
>>
>> Fixes: fe53ca54270 (mm: use early_pfn_to_nid in page_ext_init)
>> Suggested-by: Michal Hocko <mhocko@xxxxxxxxxx>
>> Signed-off-by: Qian Cai <cai@xxxxxx>
>> ---
>>
>> v3: still call page_ext_init() earlier if DEFERRED_STRUCT_PAGE_INIT=n.
>>
>> v2: postpone page_ext_init() to after page_alloc_init_late().
>>
>>  init/main.c   | 5 +++++
>>  mm/page_ext.c | 3 +--
>>  2 files changed, 6 insertions(+), 2 deletions(-)
>>
>> diff --git a/init/main.c b/init/main.c
>> index 2b7b7fe173c9..5d9904370f76 100644
>> --- a/init/main.c
>> +++ b/init/main.c
>> @@ -696,7 +696,9 @@ asmlinkage __visible void __init start_kernel(void)
>>  		initrd_start = 0;
>>  	}
>>  #endif
>> +#ifndef CONFIG_DEFERRED_STRUCT_PAGE_INIT
>>  	page_ext_init();
>> +#endif
>>  	kmemleak_init();
>>  	setup_per_cpu_pageset();
>>  	numa_policy_init();
>> @@ -1147,6 +1149,9 @@ static noinline void __init kernel_init_freeable(void)
>>  	sched_init_smp();
>>  
>>  	page_alloc_init_late();
>> +#ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT
>> +	page_ext_init();
>> +#endif
>>  
>>  	do_basic_setup();
> 
> Is this really necessary? Why cannot we simply postpone page_ext_init
> unconditioanally?

As mentioned above, "If deselected DEFERRED_STRUCT_PAGE_INIT, it is still better
to call page_ext_init() earlier, so page owner could catch more early page
allocation call sites."

> 
>>  
>> diff --git a/mm/page_ext.c b/mm/page_ext.c
>> index ae44f7adbe07..d76fd51e312a 100644
>> --- a/mm/page_ext.c
>> +++ b/mm/page_ext.c
>> @@ -399,9 +399,8 @@ void __init page_ext_init(void)
>>  			 * -------------pfn-------------->
>>  			 * N0 | N1 | N2 | N0 | N1 | N2|....
>>  			 *
>> -			 * Take into account DEFERRED_STRUCT_PAGE_INIT.
>>  			 */
>> -			if (early_pfn_to_nid(pfn) != nid)
>> +			if (pfn_to_nid(pfn) != nid)
>>  				continue;
>>  			if (init_section_page_ext(pfn, nid))
>>  				goto oom;
> 
> Also this doesn't seem to be related, right?

No, it is related. Because of this patch, page_ext_init() is called after all
the memory has already been initialized,
so no longer necessary to call early_pfn_to_nid().