From: Michal Hocko <mhocko@kernel.org>
To: Qian Cai <cai@lca.pw>
Cc: akpm@linux-foundation.org, tj@kernel.org, vdavydov.dev@gmail.com,
hannes@cmpxchg.org, guro@fb.com, cl@linux.com,
penberg@kernel.org, rientjes@google.com, linux-mm@kvack.org,
linux-kernel@vger.kernel.org, stable@vger.kernel.org
Subject: Re: [PATCH v2] mm/slub: fix a deadlock in show_slab_objects()
Date: Fri, 4 Oct 2019 14:57:01 +0200 [thread overview]
Message-ID: <20191004125701.GJ9578@dhcp22.suse.cz> (raw)
In-Reply-To: <1570192309-10132-1-git-send-email-cai@lca.pw>
On Fri 04-10-19 08:31:49, Qian Cai wrote:
> Long time ago, there fixed a similar deadlock in show_slab_objects()
> [1]. However, it is apparently due to the commits like 01fb58bcba63
> ("slab: remove synchronous synchronize_sched() from memcg cache
> deactivation path") and 03afc0e25f7f ("slab: get_online_mems for
> kmem_cache_{create,destroy,shrink}"), this kind of deadlock is back by
> just reading files in /sys/kernel/slab which will generate a lockdep
> splat below.
>
> Since the "mem_hotplug_lock" here is only to obtain a stable online node
> mask while racing with NUMA node hotplug, in the worst case, the results
> may me miscalculated while doing NUMA node hotplug, but they shall be
> corrected by later reads of the same files.
I think it is important to mention that this doesn't expose the
show_slab_objects to use-after-free. There is only a single path that
might really race here and that is the slab hotplug notifier callback
__kmem_cache_shrink (via slab_mem_going_offline_callback) but that path
doesn't really destroy kmem_cache_node data structures.
Thanks!
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2019-10-04 12:57 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-04 12:31 [PATCH v2] mm/slub: fix a deadlock in show_slab_objects() Qian Cai
2019-10-04 12:57 ` Michal Hocko [this message]
2019-10-07 8:16 ` Michal Hocko
2019-10-07 21:59 ` Andrew Morton
2019-10-08 8:47 ` Michal Hocko
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