linux-kernel - Re: [PATCH] slub: make sure struct kmem_cache

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Message-Id: <20170710133238.2afcda57ea28e020ca03c4f0@linux-foundation.org>
Date:   Mon, 10 Jul 2017 13:32:38 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Christoph Lameter <cl@...ux.com>
Cc:     Alexander Potapenko <glider@...gle.com>, dvyukov@...gle.com,
        kcc@...gle.com, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>
Subject: Re: [PATCH] slub: make sure struct kmem_cache_node is initialized
 before publication

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

> On Fri, 7 Jul 2017, Andrew Morton wrote:
> 
> > On Fri,  7 Jul 2017 10:34:08 +0200 Alexander Potapenko <glider@...gle.com> 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.