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

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Message-ID: <alpine.DEB.2.20.1707101023390.4065@east.gentwo.org>
Date:   Mon, 10 Jul 2017 10:32:13 -0500 (CDT)
From:   Christoph Lameter <cl@...ux.com>
To:     Alexander Potapenko <glider@...gle.com>
cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Dmitriy Vyukov <dvyukov@...gle.com>,
        Kostya Serebryany <kcc@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux Memory Management List <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 Mon, 10 Jul 2017, Alexander Potapenko wrote:

> >> 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?
> I've asked Andrew about READ_ONCE privately.

Please post to a mailing list and cc the maintainers?

> Since unfreeze_partials() sees uninitialized value of n->list_lock, I
> was suspecting there's a data race between unfreeze_partials() and
> init_kmem_cache_nodes().

I have not seen the details but I would suspect that this is related to
early boot issues? The list lock is initialized upon slab creation and at
that time no one can get to the kmem_cache structure.

There are a couple of boot time slabs that will temporarily be available.
and released upon boot completion.

> If so, reads and writes to s->node[node] must be acquire/release
> atomics (not actually READ_ONCE/WRITE_ONCE, but
> smp_load_acquire/smp_store_release).

Can we figure the reason for these out before proposing fixes?