Re: [PATCH stable-4.4 1/2] mm: check the return value of lookup_page_ext for all call sites

[Ben Hutchings <ben.hutchings@codethink.co.uk>]

Sorry, I see this got fixed already.

Ben.

On Tue, 2017-12-05 at 16:16 +0000, Ben Hutchings wrote:
> On Wed, 2017-11-22 at 13:09 +0100, Michal Hocko wrote:
> > From: Yang Shi <yang.shi@linaro.org>
> > 
> > commit f86e4271978bd93db466d6a95dad4b0fdcdb04f6 upstream.
> > 
> > Per the discussion with Joonsoo Kim [1], we need check the return value
> > of lookup_page_ext() for all call sites since it might return NULL in
> > some cases, although it is unlikely, i.e.  memory hotplug.
> > 
> > Tested with ltp with "page_owner=0".
> 
> [...]
> > --- a/mm/debug-pagealloc.c
> > +++ b/mm/debug-pagealloc.c
> > @@ -34,6 +34,8 @@ static inline void set_page_poison(struct page
> > *page)
> >  	struct page_ext *page_ext;
> >  
> >  	page_ext = lookup_page_ext(page);
> > +	if (page_ext)
> > +		return;
> 
> This, and the other checks added to debug-pagealloc.c, are reversed. 
> (This is specific to the 4.4 backport - in the upstream version these
> functions are in mm/page_poison.c and were patched correctly.)
> 
> Ben.
> 
> >  	__set_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
> >  }
> >  
> > @@ -42,6 +44,8 @@ static inline void clear_page_poison(struct page
> > *page)
> >  	struct page_ext *page_ext;
> >  
> >  	page_ext = lookup_page_ext(page);
> > +	if (page_ext)
> > +		return;
> >  	__clear_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
> >  }
> >  
> > @@ -50,6 +54,8 @@ static inline bool page_poison(struct page *page)
> >  	struct page_ext *page_ext;
> >  
> >  	page_ext = lookup_page_ext(page);
> > +	if (page_ext)
> > +		return false;
> >  	return test_bit(PAGE_EXT_DEBUG_POISON, &page_ext->flags);
> >  }
> >  
> 
> [...]
> 
-- 
Ben Hutchings
Software Developer, Codethink Ltd.