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

[Michal Hocko <mhocko@suse.com>]

On Tue 19-12-17 20:29:56, Tetsuo Handa wrote:
> 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;
>                          ^~~ 

http://lkml.kernel.org/r/20171215125129.2948634-1-arnd@arndb.de

-- 
Michal Hocko
SUSE Labs

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