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

KAMEZAWA Hiroyuki
2008-10-21T11:34:46Z

On Tue, 21 Oct 2008 16:59:28 +0530
Balbir Singh <balbir@linux.vnet.ibm.com> wrote:

> KAMEZAWA Hiroyuki wrote:
> > 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....
>
> Kamezawa-San,
>
> I would prefer to use alloc_bootmem() instead of vmalloc_node(). May be we can
> shift cgroups, so that we use early_init for allocating page_cgroups. What do
> you think?
>
yes, I think so. I think we'll have chance to modify this, later, after getting some
stable kernel.

Thanks,
-Kame