Re: [RFC/Patch](memory hotplug) fix null pointer access of kmem_cache_node after memory hotplug

[Yasunori Goto <y-goto@jp.fujitsu.com>]

> On Wed, 19 Sep 2007, Yasunori Goto wrote:
> 
> > build_zonelist() is called very early stage of bootstrap, But it is
> > called final stage of hot-add.
> > When build_zonelist() is called at hot-add, all kernel module can
> > use new memory of the node. So, I'm afraid like following worst case.
> > 
> >    build_zonelist()              
> >         :                     new_nodes_page = new_slab();
> >         :                         :
> >         :                         :
> >         :                     discard_slab(new_nodes_page)
> >         :                         (access kmem_cache_node)
> >         :
> >    kmem_cache_node setting,
> 
> So we cannot do this without holding off other kernel accesses since it is 
> not serialized like bootstrap. Sigh.
>
> > > > I think this "delay creation" fix is better way than it.
> > > 
> > > Looks like this is a way to on demand node structure creation?
> > 
> > Yes.
> 
> Could be useful in general if you can make that work reliably. We can just 
> start out with a single per node structure for the boot node and then add 
> others on demand?

Hmmmmm. I don't think demand node creation can be generic.
Just I would like to fix the panic.
Ok, I'll make a patch which sets kmem_cache_node before
build_zonelist() to fix panic for the present.
And I reconsider about allocation place issue later.

Thanks for your comment.

-- 
Yasunori Goto 


--
To unsubscribe, send a message with 'unsubscribe linux-mm' in
the body to majordomo@kvack.org.  For more info on Linux MM,
see: http://www.linux-mm.org/ .
Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>