On Sat, Jun 17, 2023 at 04:59:46PM +0800, Liam Ni wrote:
> On Sat, 17 Jun 2023 at 15:01, Mike Rapoport <rppt@xxxxxxxxxx> wrote:
> >
> > On Sat, Jun 17, 2023 at 02:17:58PM +0800, Liam Ni wrote:
> > > On Sat, 17 Jun 2023 at 13:44, Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
> > > >
> > > > On Sat, 17 Jun 2023 14:40:36 +1000 Liam Ni <zhiguangni01@xxxxxxxxx> wrote:
> > > >
> > > > > __nr_to_section() may return a null pointer,
> > > > > before accessing the member variable section_mem_map,
> > > > > we should first determine whether it is a null pointer.
> > > > >
> > > > > ...
> > > > >
> > > > > --- a/mm/sparse.c
> > > > > +++ b/mm/sparse.c
> > > > > @@ -258,7 +258,7 @@ static void __init memory_present(int nid, unsigned long start, unsigned long en
> > > > > set_section_nid(section, nid);
> > > > >
> > > > > ms = __nr_to_section(section);
> > > > > - if (!ms->section_mem_map) {
> > > > > + if (ms && !ms->section_mem_map) {
> > > > > ms->section_mem_map = sparse_encode_early_nid(nid) |
> > > > > SECTION_IS_ONLINE;
> > > > > __section_mark_present(ms, section);
> > > >
> > > > I'm suspecting that if __nr_to_section() returns NULL here, we should
> > > > just panic. But a null-deref gives the same information, so why change
> > > > things?
> > >
> > > Do you mean if ms is a null pointer，ms->section_mem_map will cause
> > > system panic,so we needn't change?
> >
> > Yes, if __nr_to_section ever returns NULL the system will crash anyway.
>
> I got it,do we need to print some information by panic()?
Accessing a NULL pointer will cause panic and there will be lots of
information spilled into the log anyway.
--
Sincerely yours,
Mike.
