Received-SPF: pass (google.com: domain of linux-kernel+bounces-130007-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.48.161 as permitted sender) client-ip=147.75.48.161;
Date: Wed, 3 Apr 2024 16:54:20 +0200
From: Michal =?utf-8?Q?Koutn=C3=BD?= <mkoutny@suse.com>
To: Valentin Schneider <vschneid@redhat.com>
Cc: Waiman Long <longman@redhat.com>, Tejun Heo <tj@kernel.org>, 
	Zefan Li <lizefan.x@bytedance.com>, Johannes Weiner <hannes@cmpxchg.org>, 
	Thomas Gleixner <tglx@linutronix.de>, Peter Zijlstra <peterz@infradead.org>, 
	"Rafael J. Wysocki" <rafael@kernel.org>, Len Brown <len.brown@intel.com>, Pavel Machek <pavel@ucw.cz>, 
	Shuah Khan <shuah@kernel.org>, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org, 
	linux-pm@vger.kernel.org, linux-kselftest@vger.kernel.org, 
	Frederic Weisbecker <frederic@kernel.org>, "Paul E. McKenney" <paulmck@kernel.org>, 
	Ingo Molnar <mingo@kernel.org>, Anna-Maria Behnsen <anna-maria@linutronix.de>, 
	Alex Shi <alexs@kernel.org>, Vincent Guittot <vincent.guittot@linaro.org>, 
	Barry Song <song.bao.hua@hisilicon.com>
Subject: Re: Re: [PATCH 1/2] cgroup/cpuset: Make cpuset hotplug processing
 synchronous
Message-ID: <mhwbjfm3zsoinm2eozz6d7djtflf6tbpmfzsbbsscv3u5aijtr@p2edxl6voxoa>
References: <20240401145858.2656598-1-longman@redhat.com>
 <20240401145858.2656598-2-longman@redhat.com>
 <kce74bx6aafxfuw5yovaschym4ze4kommfk74eq5totojytest@mdxnfvl2kdol>
 <548efd52-e45f-41fa-a477-bc5112d7b00c@redhat.com>
 <u3naomgv34t5rnc7pmyy4zjppgf36skeo45orss2xnqcvtrcez@m74tsl2ws76f>
 <7e62b37d-6c9c-4e55-a01a-175695475cb5@redhat.com>
 <xhsmhedbmbjz5.mognet@vschneid-thinkpadt14sgen2i.remote.csb>
Precedence: bulk
MIME-Version: 1.0
Content-Type: multipart/signed; micalg=pgp-sha512;
	protocol="application/pgp-signature"; boundary="4oauttmks2s2kyvd"
Content-Disposition: inline
In-Reply-To: <xhsmhedbmbjz5.mognet@vschneid-thinkpadt14sgen2i.remote.csb>


--4oauttmks2s2kyvd
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
Content-Transfer-Encoding: quoted-printable

On Wed, Apr 03, 2024 at 04:26:38PM +0200, Valentin Schneider <vschneid@redh=
at.com> wrote:
> Also, I gave Michal's patch a try and it looks like it's introducing a

Thank you.

>   cgroup_threadgroup_rwsem -> cpuset_mutex
> ordering from
>   cgroup_transfer_tasks_locked()
>   `\
>     percpu_down_write(&cgroup_threadgroup_rwsem);
>     cgroup_migrate()
>     `\
>       cgroup_migrate_execute()
>       `\
>         ss->can_attach() // cpuset_can_attach()
>         `\
>           mutex_lock(&cpuset_mutex);
>=20
> which is invalid, see below.

_This_ should be the right order (cpuset_mutex inside
cgroup_threadgroup_rwsem), at least in my mental model. Thus I missed
that cpuset_mutex must have been taken somewhere higher up in the
hotplug code (CPU 0 in the lockdep dump, I can't easily see where from)
:-/.

Michal

--4oauttmks2s2kyvd
Content-Type: application/pgp-signature; name="signature.asc"

-----BEGIN PGP SIGNATURE-----

iHUEABYKAB0WIQQpEWyjXuwGT2dDBqAGvrMr/1gcjgUCZg1tmgAKCRAGvrMr/1gc
jkuBAQCOU5ydo9y0TCnjqjAp/O4I1OLjgDDV/yffUbpaHCtEQwD+JkXKjW2H8u/w
FTxiJwyMy2sI6p0otQdxSBa7Bpu0Vgs=
=vBqH
-----END PGP SIGNATURE-----

--4oauttmks2s2kyvd--