linux-kernel - Re: [PATCH] mm,madvise: bugfix of madvise systemcall infinite loop under special circumstances.

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Date:   Mon, 27 Nov 2017 10:54:39 +0800
From:   郭雪楠 <guoxuenan@...wei.com>
To:     Michal Hocko <mhocko@...nel.org>
CC:     <akpm@...ux-foundation.org>, <minchan@...nel.org>,
        <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        <rppt@...ux.vnet.ibm.com>, <yi.zhang@...wei.com>,
        <miaoxie@...wei.com>, <aarcange@...hat.com>,
        <mgorman@...hsingularity.net>, <kirill.shutemov@...ux.intel.com>,
        <rientjes@...gle.com>, <khandual@...ux.vnet.ibm.com>,
        <riel@...hat.com>, <hillf.zj@...baba-inc.com>, <shli@...com>
Subject: Re: [PATCH] mm,madvise: bugfix of madvise systemcall infinite loop
 under special circumstances.

Hi,Michal, Whether  need me to modify according your modification and 
resubmit a new patch?

在 2017/11/25 9:52, 郭雪楠 写道:
> Yes , your modification is much better! thanks.
> 
> 在 2017/11/24 21:08, Michal Hocko 写道:
>> On Fri 24-11-17 20:51:29, 郭雪楠 wrote:
>>> Sorry,I explained  wrong before. But,I've tested using trinity in DAX
>>> mode,and I'am sure it has possibility of triggering an soft lockup. I 
>>> have
>>> encountered the problem of endless loop here .
>>>
>>> I had a little problem here,I correct it .
>>> under Initial state :
>>> [ start = vam->vm_start < vam->vm_end < end ]
>>>
>>> When [start = vam->vm_start] the program enters  for{;;} loop
>>> ,find_vma_prev() will set the pointer vma and the pointer prev (prev =
>>> vam->vm_prev ). Normally ,madvise_vma() will always move the pointer 
>>> prev
>>> ,but when use DAX mode , it will never update .
>> [...]
>>> if (prev) // here prev not NULL,it will always enter this branch ..
>>>     vma = prev->vm_next;
>>> else    /* madvise_remove dropped mmap_sem */
>>>     vma = find_vma(current->mm, start);
>>
>> You are right! My fault, I managed to confuse myself in the code flow.
>> It really looks like this has been broken for more than 10 years since
>> fe77ba6f4f97 ("[PATCH] xip: madvice/fadvice: execute in place").
>>
>> Maybe the following would be more readable and less error prone?
>> ---
>> diff --git a/mm/madvise.c b/mm/madvise.c
>> index 375cf32087e4..a631c414f915 100644
>> --- a/mm/madvise.c
>> +++ b/mm/madvise.c
>> @@ -276,30 +276,26 @@ static long madvise_willneed(struct 
>> vm_area_struct *vma,
>>   {
>>       struct file *file = vma->vm_file;
>> +    *prev = vma;
>>   #ifdef CONFIG_SWAP
>>       if (!file) {
>> -        *prev = vma;
>>           force_swapin_readahead(vma, start, end);
>>           return 0;
>>       }
>> -    if (shmem_mapping(file->f_mapping)) {
>> -        *prev = vma;
>> +    if (shmem_mapping(file->f_mapping))
>>           force_shm_swapin_readahead(vma, start, end,
>>                       file->f_mapping);
>>           return 0;
>> -    }
>>   #else
>>       if (!file)
>>           return -EBADF;
>>   #endif
>> -    if (IS_DAX(file_inode(file))) {
>> +    if (IS_DAX(file_inode(file)))
>>           /* no bad return value, but ignore advice */
>>           return 0;
>> -    }
>> -    *prev = vma;
>>       start = ((start - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
>>       if (end > vma->vm_end)
>>           end = vma->vm_end;
>>