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

Zaslonko Mikhail
2018-12-11T15:24:44Z

Hello,

On 11.12.2018 02:50, Wei Yang wrote:
> 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@linux.ibm.com>
>>>> Reviewed-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
>>>> Cc: <stable@vger.kernel.org>
>>>> ---
>>>> 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?
>

No you don't. I guess there might be deviations depending on the architecture (I am on s390).
As I understand, memory block size is 384 Mb on your system and memory9 is the last block on the list?
BTW, do you have CONFIG_DEBUG_VM and CONFIG_DEBUG_VM_PGFLAGS on?

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