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

[Ingo Molnar <mingo@elte.hu>]

* KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:

> On Tue, 21 Oct 2008 13:28:43 +0200
> Ingo Molnar <mingo@elte.hu> wrote:
> 
> > 
> > * KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> 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....
> > 
> > okay. So what is needed for the crash is:
> > 
> >  CONFIG_CGROUPS=y
> >  CONFIG_CGROUP_MEM_RES_CTLR=y
> > 
>
> yes. maybe.  I think you can avoid crash by cgroup_disable=memory boot 
> option. But Nishimura reports he cannot boot with 
> cgroup_disable=memory. So I wonder there may be something other. But 
> calling alloc_bootmem() here should be avoided.

the patch did the trick for my test-setup - no more crash during bootup.

Tested-by: Ingo Molnar <mingo@elte.hu>

(but i cannot vouch for the completeness of the fix, other than observe 
that it boots and works fine.)

	Ingo

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