On Mon 21-01-19 11:38:49, Qian Cai wrote:
>
>
> On 1/21/19 4:53 AM, Michal Hocko wrote:
> > On Thu 17-01-19 21:16:50, Qian Cai wrote:
[...]
> >> Fixes: 2d070eab2e82 ("mm: consider zone which is not fully populated to
> >> have holes")
> >
> > Did you mean
> > Fixes: 9f1eb38e0e11 ("mm, kmemleak: little optimization while scanning")
>
> No, pfn_to_online_page() missed a few checks compared to pfn_valid() at least on
> arm64 where the returned pfn is no longer valid (where pfn_valid() will skip those).
>
> 2d070eab2e82 introduced pfn_to_online_page(), so it was targeted to fix it.
But it is 9f1eb38e0e11 which has replaced pfn_valid by
pfn_to_online_page.
>
> >
> >> Signed-off-by: Qian Cai <cai@xxxxxx>
> >> ---
> >> include/linux/memory_hotplug.h | 2 +-
> >> 1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
> >> index 07da5c6c5ba0..b8b36e6ac43b 100644
> >> --- a/include/linux/memory_hotplug.h
> >> +++ b/include/linux/memory_hotplug.h
> >> @@ -26,7 +26,7 @@ struct vmem_altmap;
> >> struct page *___page = NULL; \
> >> unsigned long ___nr = pfn_to_section_nr(pfn); \
> >> \
> >> - if (___nr < NR_MEM_SECTIONS && online_section_nr(___nr))\
> >> + if (online_section_nr(___nr) && pfn_valid(pfn)) \
> >> ___page = pfn_to_page(pfn); \
> >
> > Why have you removed the bound check? Is this safe?
> > Regarding the fix, I am not really sure TBH. If the secion is online
> > then we assume all struct pages to be initialized. If anything this
> > should be limited to werid arches which might have holes so
> > pfn_valid_within().
>
> It looks to me at least on arm64 and x86_64, it has done this check in
> pfn_valid() already.
>
> if (pfn_to_section_nr(pfn) >= NR_MEM_SECTIONS)
> return 0
But an everflow could happen before pfn_valid is evaluated, no?
--
Michal Hocko
SUSE Labs
