From: Dima Zavin <dmitriyz@waymo.com>
To: Christopher Lameter <cl@linux.com>
Cc: Mel Gorman <mgorman@suse.de>,
Andrew Morton <akpm@linux-foundation.org>,
Li Zefan <lizefan@huawei.com>, Pekka Enberg <penberg@kernel.org>,
David Rientjes <rientjes@google.com>,
Joonsoo Kim <iamjoonsoo.kim@lge.com>,
cgroups@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>,
linux-mm@kvack.org, Cliff Spradlin <cspradlin@waymo.com>
Subject: Re: [RFC PATCH] mm/slub: fix a deadlock due to incomplete patching of cpusets_enabled()
Date: Wed, 26 Jul 2017 12:52:56 -0700 [thread overview]
Message-ID: <CAPz4a6AtLNf8sJzA2Ux-ta4B+_YLdG7OWEMvJij_Zguo0Q1sjw@mail.gmail.com> (raw)
In-Reply-To: <alpine.DEB.2.20.1707261158560.9311@nuc-kabylake>
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On Wed, Jul 26, 2017 at 10:02 AM, Christopher Lameter <cl@linux.com> wrote:
> 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?
>
Thanks for the quick reply!
I can turn the cookie into a uint64, put the sequence into the low order 32
bits and put the enabled state into bit 33 (or 63 :) ). Then retry will not
query cpusets_enabled() and will just look at the enabled bit. This means
that *_retry will always have a conditional jump (i.e. lose the whole
static_branch optimization) but maybe that's ok since that's pretty rare
and the *_begin() will still benefit from it?
--Dima
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next prev parent reply other threads:[~2017-07-26 19:52 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-07-26 16:50 Dima Zavin
2017-07-26 17:02 ` Christopher Lameter
2017-07-26 19:52 ` Dima Zavin [this message]
2017-07-26 19:54 ` Dima Zavin
2017-07-27 16:46 ` [PATCH v2] cpuset: " Dima Zavin
2017-07-27 19:48 ` Andrew Morton
2017-07-27 21:41 ` Dima Zavin
2017-07-27 19:51 ` Andrew Morton
2017-07-27 21:41 ` Dima Zavin
2017-07-28 7:45 ` Vlastimil Babka
2017-07-28 8:48 ` Dima Zavin
2017-07-28 9:30 ` Peter Zijlstra
2017-07-28 14:05 ` Vlastimil Babka
2017-07-28 16:52 ` Dima Zavin
2017-07-31 4:01 ` [PATCH v3] " Dima Zavin
2017-07-31 4:04 ` Dima Zavin
2017-07-31 8:02 ` Vlastimil Babka
2017-07-31 9:05 ` Dima Zavin
2017-07-29 4:56 ` [PATCH v2] " kbuild test robot
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