linux-kernel - Re: [RFC PATCH] mm/slub: fix a deadlock due to incomplete patching of cpusets

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Message-ID: <alpine.DEB.2.20.1707261158560.9311@nuc-kabylake>
Date:   Wed, 26 Jul 2017 12:02:17 -0500 (CDT)
From:   Christopher Lameter <cl@...ux.com>
To:     Dima Zavin <dmitriyz@...mo.com>
cc:     Mel Gorman <mgorman@...e.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Li Zefan <lizefan@...wei.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>, cgroups@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Cliff Spradlin <cspradlin@...mo.com>
Subject: Re: [RFC PATCH] mm/slub: fix a deadlock due to incomplete patching
 of cpusets_enabled()

On Wed, 26 Jul 2017, Dima Zavin wrote:

> The fix is to cache the value that's returned by cpusets_enabled() at the
> top of the loop, and only operate on the seqlock (both begin and retry) if
> it was true.

I think the proper fix would be to ensure that the calls to
read_mems_allowed_{begin,retry} cannot cause the deadlock. Otherwise you
have to fix this in multiple places.

Maybe read_mems_allowed_* can do some form of synchronization or *_retry
can implictly rely on the results of cpusets_enabled() by *_begin?