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From:   Qian Cai <cai@lca.pw>
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Subject: Re: [PATCH v2 4/4] mm/slub: Fix sysfs shrink circular locking dependency
Date:   Mon, 27 Apr 2020 22:11:13 -0400
Message-Id: <28BB8A1C-CFDF-4F5A-8686-537C3CE04818@lca.pw>
References: <dbbfe685-7374-9a96-b7c2-684142746e30@redhat.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Christoph Lameter <cl@linux.com>,
        Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>,
        Vladimir Davydov <vdavydov.dev@gmail.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, cgroups@vger.kernel.org,
        Juri Lelli <juri.lelli@redhat.com>
In-Reply-To: <dbbfe685-7374-9a96-b7c2-684142746e30@redhat.com>
To:     Waiman Long <longman@redhat.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


> On Apr 27, 2020, at 9:39 PM, Waiman Long <longman@redhat.com> wrote:
>=20
> The sequence that was prevented by this patch is "kn->count --> mem_hotplu=
g_lock.rwsem". This sequence isn't directly in the splat. Once this link is b=
roken, the 3-lock circular loop cannot be formed. Maybe I should modify the c=
ommit log to make this point more clear.

I don=E2=80=99t know what you are talking about. Once trylock succeed once, y=
ou will have kn->count =E2=80=94> cpu/memory_hotplug_lock.=