[PATCH] mm: pagewalk: prevent positive return value of walk_page_test() from being passed to callers (Re: [PATCH] mm: fix do_mbind return value)

[Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>]

# CCed Andrew and linux-mm

On Wed, Mar 04, 2015 at 10:53:27PM -0800, David Rientjes wrote:
> On Wed, 4 Mar 2015, Kazutomo Yoshii wrote:
> 
> > I noticed that numa_alloc_onnode() failed to allocate memory on a
> > specified node in v4.0-rc1. I added a code to check the return value
> > of walk_page_range() in queue_pages_range() so that do_mbind() only
> > returns an error number or zero.
> > 
> 
> I assume this is libnuma-2.0.10?
> 
> > Signed-off-by: Kazutomo Yoshii <kazutomo.yoshii@gmail.com>
> > ---
> >  mm/mempolicy.c | 6 +++++-
> >  1 file changed, 5 insertions(+), 1 deletion(-)
> > 
> > diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> > index 4721046..ea79171 100644
> > --- a/mm/mempolicy.c
> > +++ b/mm/mempolicy.c
> > @@ -644,6 +644,7 @@ queue_pages_range(struct mm_struct *mm, unsigned long start, unsigned long end,
> >  		.nmask = nodes,
> >  		.prev = NULL,
> >  	};
> > +	int err;
> >  	struct mm_walk queue_pages_walk = {
> >  		.hugetlb_entry = queue_pages_hugetlb,
> >  		.pmd_entry = queue_pages_pte_range,
> > @@ -652,7 +653,10 @@ queue_pages_range(struct mm_struct *mm, unsigned long start, unsigned long end,
> >  		.private = &qp,
> >  	};
> >  -	return walk_page_range(start, end, &queue_pages_walk);
> > +	err = walk_page_range(start, end, &queue_pages_walk);
> > +	if (err < 0)
> > +		return err;
> > +	return 0;
> >  }
> >   /*
> 
> I'm afraid I don't think this is the right fix, if walk_page_range() 
> returns a positive value then it should be supplied by one of the 
> callbacks in the struct mm_walk, which none of these happen to do.  I 
> think this may be a problem with commit 6f4576e3687b ("mempolicy: apply 
> page table walker on queue_pages_range()"), so let's add Naoya to the 
> thread.

Thank you for reporting/forwarding, Yoshii-san and David.

This bug is in the pagewalk's common path, and the following patch should
fix it.

Thanks,
Naoya Horiguchi
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