Re: [PATCH] mm: thp: use down_read_trylock in khugepaged to avoid long block

[Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>]

On 2017/12/15 4:53, Yang Shi wrote:
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index ea4ff25..ecc2b68 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -1674,7 +1674,12 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages,
>  	spin_unlock(&khugepaged_mm_lock);
>  
>  	mm = mm_slot->mm;
> -	down_read(&mm->mmap_sem);
> +	/*
> + 	 * Not wait for semaphore to avoid long time waiting, just move
> + 	 * to the next mm on the list.
> + 	 */
> +	if (unlikely(!down_read_trylock(&mm->mmap_sem)))
> +		goto breakouterloop_mmap_sem;
>  	if (unlikely(khugepaged_test_exit(mm)))
>  		vma = NULL;
>  	else
> 

You are jumping before initializing vma.

mm/khugepaged.c: In function a??khugepageda??:
mm/khugepaged.c:1757:31: warning: a??vmaa?? may be used uninitialized in this function [-Wmaybe-uninitialized]
  if (khugepaged_test_exit(mm) || !vma) {
      ~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~
mm/khugepaged.c:1659:25: note: a??vmaa?? was declared here
  struct vm_area_struct *vma;
                         ^~~ 

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