Re: [PATCH] slub: make sure struct kmem_cache_node is initialized before publication

[Andrew Morton]

On Fri, 7 Jul 2017 18:18:31 -0500 (CDT) Christoph Lameter <cl@xxxxxxxxx> wrote:

> On Fri, 7 Jul 2017, Andrew Morton wrote:
> 
> > On Fri,  7 Jul 2017 10:34:08 +0200 Alexander Potapenko <glider@xxxxxxxxxx> wrote:
> >
> > > --- a/mm/slub.c
> > > +++ b/mm/slub.c
> > > @@ -3389,8 +3389,8 @@ static int init_kmem_cache_nodes(struct kmem_cache *s)
> > >  			return 0;
> > >  		}
> > >
> > > -		s->node[node] = n;
> > >  		init_kmem_cache_node(n);
> > > +		s->node[node] = n;
> > >  	}
> > >  	return 1;
> > >  }
> >
> > If this matters then I have bad feelings about free_kmem_cache_nodes():
> 
> At creation time the kmem_cache structure is private and no one can run a
> free operation.
> 
> > Inviting a use-after-free?  I guess not, as there should be no way
> > to look up these items at this stage.
> 
> Right.

Still.   It looks bad, and other sites do these things in the other order.

> > Could the slab maintainers please take a look at these and also have a
> > think about Alexander's READ_ONCE/WRITE_ONCE question?
> 
> Was I cced on these?

It's all on linux-mm.