On Tue 05-12-17 16:16:35, Ben Hutchings wrote: > On Wed, 2017-11-22 at 13:09 +0100, Michal Hocko wrote: > > From: Yang Shi <yang.shi@xxxxxxxxxx> > > > > 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.) Yes, I've sent a fixup and Greg has queued it up as 0208fabf7256245125fbabf03207a0da4000ea2d -- Michal Hocko SUSE Labs