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Date:   Tue, 10 Dec 2019 18:32:37 +0000 (UTC)
From:   Christopher Lameter <cl@linux.com>
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To:     Qian Cai <cai@lca.pw>
cc:     Daniel Wagner <dwagner@suse.de>, Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: Re: lockdep warns: cpu_hotplug_lock.rw_sem --> slab_mutex -->
 kn->count#39
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On Mon, 9 Dec 2019, Qian Cai wrote:

> It happens to me too with a probably easier to trigger deadlock. Basically, we have,
>
> memcg_create_kmem_cache():
> cpu_hotplug_lock.rw_sem/mem_hotplug_lock.rw_sem —> kn->count

Right. Memcg runs this function at cgroup creation time. sysfs
initialization was designed to run a at boot. So the sysfs initialization
needs a rewrite of its serialization for the memcg case. We cannot loop
over the list of all kmem caches holding the slab_mutex anymore.

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