Re: [PATCH 1/1] mm, memory_hotplug: Initialize struct pages for the full memory section

[Wei Yang]

On Mon, Dec 10, 2018 at 05:14:36PM +0100, Zaslonko Mikhail wrote:
>Hello,
>
>On 10.12.2018 16:10, Wei Yang wrote:
>> On Mon, Dec 10, 2018 at 02:07:12PM +0100, Mikhail Zaslonko wrote:
>>> If memory end is not aligned with the sparse memory section boundary, the
>>> mapping of such a section is only partly initialized. This may lead to
>>> VM_BUG_ON due to uninitialized struct page access from
>>> is_mem_section_removable() or test_pages_in_a_zone() function triggered by
>>> memory_hotplug sysfs handlers:
>>>
>>> page:000003d082008000 is uninitialized and poisoned
>>> page dumped because: VM_BUG_ON_PAGE(PagePoisoned(p))
>>> Call Trace:
>>> ([<0000000000385b26>] test_pages_in_a_zone+0xde/0x160)
>>>  [<00000000008f15c4>] show_valid_zones+0x5c/0x190
>>>  [<00000000008cf9c4>] dev_attr_show+0x34/0x70
>>>  [<0000000000463ad0>] sysfs_kf_seq_show+0xc8/0x148
>>>  [<00000000003e4194>] seq_read+0x204/0x480
>>>  [<00000000003b53ea>] __vfs_read+0x32/0x178
>>>  [<00000000003b55b2>] vfs_read+0x82/0x138
>>>  [<00000000003b5be2>] ksys_read+0x5a/0xb0
>>>  [<0000000000b86ba0>] system_call+0xdc/0x2d8
>>> Last Breaking-Event-Address:
>>>  [<0000000000385b26>] test_pages_in_a_zone+0xde/0x160
>>> Kernel panic - not syncing: Fatal exception: panic_on_oops
>>>
>>> Fix the problem by initializing the last memory section of the highest zone
>>> in memmap_init_zone() till the very end, even if it goes beyond the zone
>>> end.
>>>
>>> Signed-off-by: Mikhail Zaslonko <zaslonko@xxxxxxxxxxxxx>
>>> Reviewed-by: Gerald Schaefer <gerald.schaefer@xxxxxxxxxx>
>>> Cc: <stable@xxxxxxxxxxxxxxx>
>>> ---
>>> mm/page_alloc.c | 15 +++++++++++++++
>>> 1 file changed, 15 insertions(+)
>>>
>>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>>> index 2ec9cc407216..41ef5508e5f1 100644
>>> --- a/mm/page_alloc.c
>>> +++ b/mm/page_alloc.c
>>> @@ -5542,6 +5542,21 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone,
>>> 			cond_resched();
>>> 		}
>>> 	}
>>> +#ifdef CONFIG_SPARSEMEM
>>> +	/*
>>> +	 * If there is no zone spanning the rest of the section
>>> +	 * then we should at least initialize those pages. Otherwise we
>>> +	 * could blow up on a poisoned page in some paths which depend
>>> +	 * on full sections being initialized (e.g. memory hotplug).
>>> +	 */
>>> +	if (end_pfn == max_pfn) {
>>> +		while (end_pfn % PAGES_PER_SECTION) {
>>> +			__init_single_page(pfn_to_page(end_pfn), end_pfn, zone,
>>> +					   nid);
>>> +			end_pfn++;
>>> +		}
>>> +	}
>>> +#endif
>> 
>> If my understanding is correct, end_pfn is not a valid range.
>> 
>> memmap_init_zone() initialize the range [start_pfn, start_pfn + size). I
>> am afraid this will break the syntax. 
>> 
>> And max_pfn is also not a valid one. For example, on x86,
>I used pfn_max here to check for the highest zone. What would be a better way? 
>
>> update_end_of_memory_vars() will update max_pfn, which is calculated by:
>> 
>>     end_pfn = PFN_UP(start + size);
>> 
>> BTW, as you mentioned this apply to hotplug case. And then why this couldn't
>> happen during boot up? What differ these two cases?
>
>Well, the pages left uninitialized during bootup (initial problem), but the panic itself takes 
>place when we try to process memory_hotplug sysfs attributes (thus triggering sysfs handlers). 
>You can find more details in the original thread:
>https://marc.info/?t=153658306400001&r=1&w=2
>

Thanks.

I took a look into the original thread and try to reproduce this on x86.

My step is:

  1. config page_poisoning
  2. use kernel parameter mem=3075M
  3. cat the last memory block device sysfs file removable
     eg. when mem is 3075, cat memory9/removable

I don't see the Call trace. Do I miss something to reproduce it?

>> 
>>> }
>>>
>>> #ifdef CONFIG_ZONE_DEVICE
>>> -- 
>>> 2.16.4
>> 
>
>Thanks,
>Mikhail Zaslonko

-- 
Wei Yang
Help you, Help me