Re: list corruption in deferred_split_scan()

[Qian Cai]

> On Jul 12, 2019, at 3:12 PM, Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx> 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 todayâs linux-next.