linux-kernel - Re: [PATCH v2 4/4] mm/slub: Fix sysfs shrink circular locking dependency

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Message-Id: <28BB8A1C-CFDF-4F5A-8686-537C3CE04818@lca.pw>
Date:   Mon, 27 Apr 2020 22:11:13 -0400
From:   Qian Cai <cai@....pw>
To:     Waiman Long <longman@...hat.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Johannes Weiner <hannes@...xchg.org>,
        Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
        Juri Lelli <juri.lelli@...hat.com>
Subject: Re: [PATCH v2 4/4] mm/slub: Fix sysfs shrink circular locking dependency



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

I don’t know what you are talking about. Once trylock succeed once, you will have kn->count —> cpu/memory_hotplug_lock.