linux-kernel - Re: list corruption in deferred_split

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Date:   Thu, 18 Jul 2019 17:59:50 -0700
From:   Yang Shi <yang.shi@...ux.alibaba.com>
To:     Qian Cai <cai@....pw>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux MM <linux-mm@...ck.org>, linux-kernel@...r.kernel.org
Subject: Re: list corruption in deferred_split_scan()



On 7/18/19 5:54 PM, Qian Cai wrote:
>
>> On Jul 12, 2019, at 3:12 PM, Yang Shi <yang.shi@...ux.alibaba.com> wrote:
>>
>>
>>
>> On 7/11/19 2:07 PM, Qian Cai wrote:
>>> On Wed, 2019-07-10 at 17:16 -0700, Yang Shi wrote:
>>>> Hi Qian,
>>>>
>>>>
>>>> Thanks for reporting the issue. But, I can't reproduce it on my machine.
>>>> Could you please share more details about your test? How often did you
>>>> run into this problem?
>>> I can almost reproduce it every time on a HPE ProLiant DL385 Gen10 server. Here
>>> is some more information.
>>>
>>> # cat .config
>>>
>>> https://raw.githubusercontent.com/cailca/linux-mm/master/x86.config
>> I tried your kernel config, but I still can't reproduce it. My compiler doesn't have retpoline support, so CONFIG_RETPOLINE is disabled in my test, but I don't think this would make any difference for this case.
>>
>> According to the bug call trace in the earlier email, it looks deferred _split_scan lost race with put_compound_page. The put_compound_page would call free_transhuge_page() which delete the page from the deferred split queue, but it may still appear on the deferred list due to some reason.
>>
>> Would you please try the below patch?
>>
>> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
>> index b7f709d..66bd9db 100644
>> --- a/mm/huge_memory.c
>> +++ b/mm/huge_memory.c
>> @@ -2765,7 +2765,7 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
>>          if (!mapcount && page_ref_freeze(head, 1 + extra_pins)) {
>>                  if (!list_empty(page_deferred_list(head))) {
>>                          ds_queue->split_queue_len--;
>> -                       list_del(page_deferred_list(head));
>> +                       list_del_init(page_deferred_list(head));
>>                  }
>>                  if (mapping)
>>                          __dec_node_page_state(page, NR_SHMEM_THPS);
>> @@ -2814,7 +2814,7 @@ void free_transhuge_page(struct page *page)
>>          spin_lock_irqsave(&ds_queue->split_queue_lock, flags);
>>          if (!list_empty(page_deferred_list(page))) {
>>                  ds_queue->split_queue_len--;
>> -               list_del(page_deferred_list(page));
>> +               list_del_init(page_deferred_list(page));
>>          }
>>          spin_unlock_irqrestore(&ds_queue->split_queue_lock, flags);
>>          free_compound_page(page);
> Unfortunately, I am no longer be able to reproduce the original list corruption with today’s linux-next.

It is because the patches have been dropped from -mm tree by Andrew due 
to this problem I guess. You have to use next-20190711, or apply the 
patches on today's linux-next.