Re: [memcg BUG] unable to handle kernel NULL pointer derefence at 00000000

KAMEZAWA Hiroyuki
2008-10-21T11:23:52Z

On Tue, 21 Oct 2008 13:19:51 +0200
Ingo Molnar <mingo@elte.hu> wrote:

>
> * Li Zefan <lizf@cn.fujitsu.com> wrote:
>
> > > Oh! thanks...but it seems pc->page is NULL in the middle of ZONE_NORMAL..
> > > ==
> > > Normal 0x00001000 -> 0x000373fe
> > > ==
> > > This is appearently in the range of page_cgroup initialization.
> > > (if pgdat->node_page_cgroup is initalized correctly...)
> > >
> > > I think write to page_cgroup->page happens only at initialization.
> > > Hmm ? not initilization failure but curruption ?
> > >
> >
> > Yes, curruption. I didn't find informatation about initialization failure.
> >
> > > What happens if replacing __alloc_bootmem() with vmalloc() in page_cgroup.c init ?
> > >
> >
> > So I did this change, and the box booted up without any problem.
> >
> > diff --git a/mm/page_cgroup.c b/mm/page_cgroup.c
> > index 5d86550..82a30b1 100644
> > --- a/mm/page_cgroup.c
> > +++ b/mm/page_cgroup.c
> > @@ -48,8 +48,7 @@ static int __init alloc_node_page_cgroup(int nid)
> >
> > table_size = sizeof(struct page_cgroup) * nr_pages;
> >
> > - base = __alloc_bootmem_node_nopanic(NODE_DATA(nid),
> > - table_size, PAGE_SIZE, __pa(MAX_DMA_ADDRESS));
> > + base = vmalloc_node(table_size, nid);
> > if (!base)
> > return -ENOMEM;
>
> i have this:
>
> CONFIG_FAILSLAB=y
> CONFIG_FAIL_PAGE_ALLOC=y
> # CONFIG_FAIL_MAKE_REQUEST is not set
> CONFIG_FAIL_IO_TIMEOUT=y
>
> so the bug was perhaps that the __alloc_bootmem_node_nopanic() failed
> and this code continued silently? vmalloc_node() probably is more
> agressive about allocating memory.
>
Sorry. I think I cannot use alloc_bootmem() at this point because
it's too late in init-path. (we can use usual page allocator)
So, just replacing alloc_bootmem() with vmalloc_node() is a fix....

Thanks,
-Kame