From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1161146AbcA1MrH (ORCPT <rfc822;w@1wt.eu>);
	Thu, 28 Jan 2016 07:47:07 -0500
Received: from mail-wm0-f49.google.com ([74.125.82.49]:36868 "EHLO
	mail-wm0-f49.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S965838AbcA1MrD (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Thu, 28 Jan 2016 07:47:03 -0500
Date: Thu, 28 Jan 2016 13:47:00 +0100
From: Thierry Reding <thierry.reding@gmail.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Tejun Heo <tj@kernel.org>, Ulrich Obergfell <uobergfe@redhat.com>,
        Ingo Molnar <mingo@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org, kernel-team@fb.com,
        Jon Hunter <jonathanh@nvidia.com>, linux-tegra@vger.kernel.org,
        rmk+kernel@arm.linux.org.uk
Subject: Re: [PATCH] workqueue: warn if memory reclaim tries to flush
 !WQ_MEM_RECLAIM workqueue
Message-ID: <20160128124700.GA26897@ulmo>
References: <20151203002810.GJ19878@mtj.duckdns.org>
 <20151203093350.GP17308@twins.programming.kicks-ass.net>
 <20151203100018.GO11639@twins.programming.kicks-ass.net>
 <20151203144811.GA27463@mtj.duckdns.org>
 <20151203150442.GR17308@twins.programming.kicks-ass.net>
 <20151203150604.GC27463@mtj.duckdns.org>
 <20151203192616.GJ27463@mtj.duckdns.org>
 <20160126173843.GA11115@ulmo.nvidia.com>
 <20160128101210.GC6357@twins.programming.kicks-ass.net>
MIME-Version: 1.0
Content-Type: multipart/signed; micalg=pgp-sha256;
	protocol="application/pgp-signature"; boundary="5mCyUwZo2JvN/JJP"
Content-Disposition: inline
In-Reply-To: <20160128101210.GC6357@twins.programming.kicks-ass.net>
User-Agent: Mutt/1.5.24 (2015-08-30)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org


--5mCyUwZo2JvN/JJP
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
Content-Transfer-Encoding: quoted-printable

On Thu, Jan 28, 2016 at 11:12:10AM +0100, Peter Zijlstra wrote:
> On Tue, Jan 26, 2016 at 06:38:43PM +0100, Thierry Reding wrote:
> > > Task or work item involved in memory reclaim trying to flush a
> > > non-WQ_MEM_RECLAIM workqueue or one of its work items can lead to
> > > deadlock.  Trigger WARN_ONCE() if such conditions are detected.
> > I've started noticing the following during boot on some of the devices I
> > work with:
> >=20
> > [    4.723705] WARNING: CPU: 0 PID: 6 at kernel/workqueue.c:2361 check_=
flush_dependency+0x138/0x144()
> > [    4.736818] workqueue: WQ_MEM_RECLAIM deferwq:deferred_probe_work_fu=
nc is flushing !WQ_MEM_RECLAIM events:lru_add_drain_per_cpu
> > [    4.748099] Modules linked in:
> > [    4.751342] CPU: 0 PID: 6 Comm: kworker/u8:0 Not tainted 4.5.0-rc1-0=
0018-g420fc292d9c7 #1
> > [    4.759504] Hardware name: NVIDIA Tegra SoC (Flattened Device Tree)
> > [    4.765762] Workqueue: deferwq deferred_probe_work_func
> > [    4.771004] [<c0017acc>] (unwind_backtrace) from [<c0013134>] (show_=
stack+0x10/0x14)
> > [    4.778746] [<c0013134>] (show_stack) from [<c0245f18>] (dump_stack+=
0x94/0xd4)
> > [    4.785966] [<c0245f18>] (dump_stack) from [<c0026f9c>] (warn_slowpa=
th_common+0x80/0xb0)
> > [    4.794048] [<c0026f9c>] (warn_slowpath_common) from [<c0026ffc>] (w=
arn_slowpath_fmt+0x30/0x40)
> > [    4.802736] [<c0026ffc>] (warn_slowpath_fmt) from [<c00390b8>] (chec=
k_flush_dependency+0x138/0x144)
> > [    4.811769] [<c00390b8>] (check_flush_dependency) from [<c0039ca0>] =
(flush_work+0x50/0x15c)
> > [    4.820112] [<c0039ca0>] (flush_work) from [<c00c51b0>] (lru_add_dra=
in_all+0x130/0x180)
> > [    4.828110] [<c00c51b0>] (lru_add_drain_all) from [<c00f728c>] (migr=
ate_prep+0x8/0x10)
>=20
> Right, also, I think it makes sense to do lru_add_drain_all() from a
> WQ_MEM_RECLAIM workqueue, it is, after all, aiding in getting memory
> freed.
>=20
> Does something like the below cure things?
>=20
> TJ does this make sense to you?
>=20
> ---
>  mm/swap.c | 11 ++++++++++-
>  1 file changed, 10 insertions(+), 1 deletion(-)
>=20
> diff --git a/mm/swap.c b/mm/swap.c
> index 09fe5e97714a..a3de016b2a9d 100644
> --- a/mm/swap.c
> +++ b/mm/swap.c
> @@ -666,6 +666,15 @@ static void lru_add_drain_per_cpu(struct work_struct=
 *dummy)
> =20
>  static DEFINE_PER_CPU(struct work_struct, lru_add_drain_work);
> =20
> +static struct workqueue_struct *lru_wq;
> +
> +static int __init lru_init(void)
> +{
> +	lru_wq =3D create_workqueue("lru");
> +	return 0;
> +}
> +early_initcall(lru_init);
> +
>  void lru_add_drain_all(void)
>  {
>  	static DEFINE_MUTEX(lock);
> @@ -685,7 +694,7 @@ void lru_add_drain_all(void)
>  		    pagevec_count(&per_cpu(lru_deactivate_pvecs, cpu)) ||
>  		    need_activate_page_drain(cpu)) {
>  			INIT_WORK(work, lru_add_drain_per_cpu);
> -			schedule_work_on(cpu, work);
> +			queue_work_on(cpu, &lru_wq, work);
                                           ^

This ampersand is too much here and causes a compile-time warning.
Removing it and booting the resulting kernel doesn't trigger the
WQ_MEM_RECLAIM warning anymore, though.

Tested on top of next-20160128.

Thanks,
Thierry

--5mCyUwZo2JvN/JJP
Content-Type: application/pgp-signature; name="signature.asc"

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v2
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=QRH0
-----END PGP SIGNATURE-----

--5mCyUwZo2JvN/JJP--