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SubjectRe: [PATCH] mm,madvise: bugfix of madvise systemcall infinite loop under special circumstances.
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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;
>>

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