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

Wei Yang
2018-12-11T22:14:23Z

On Tue, Dec 11, 2018 at 04:23:05PM +0100, Zaslonko Mikhail wrote:
>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?

Sorry, my calculation is not correct. The last memory_block is 23
instead of 9.

>BTW, do you have CONFIG_DEBUG_VM and CONFIG_DEBUG_VM_PGFLAGS on?
>

Yes, I have set it:

CONFIG_DEBUG_VM=y
CONFIG_DEBUG_VM_PGFLAGS=y

And the kernel cmdline is:

BOOT_IMAGE=/vmlinuz-4.20.0-rc5+ root=UUID=98aa84d6-9ba6-4033-ab91-9ca6fe3dd74f ro \
resume=UUID=b7c21053-d9c1-4e58-8488-7d385f8ee107 console=ttyS0 \
LANG=en_US.UTF-8 mem=3075M

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

--
Wei Yang
Help you, Help me