Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
From:   "Zhang, Qiang1" <qiang1.zhang@intel.com>
To:     Frederic Weisbecker <frederic@kernel.org>
CC:     "paulmck@kernel.org" <paulmck@kernel.org>,
        "quic_neeraju@quicinc.com" <quic_neeraju@quicinc.com>,
        "joel@joelfernandes.org" <joel@joelfernandes.org>,
        "rcu@vger.kernel.org" <rcu@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH v2] rcu: Remove impossible wakeup rcu GP kthread action
 from rcu_report_qs_rdp()
Thread-Topic: [PATCH v2] rcu: Remove impossible wakeup rcu GP kthread action
 from rcu_report_qs_rdp()
Thread-Index: AQHZKkbpBc99toz8qk+05nvOIQVTQ66ipEaAgAEhpAA=
Date:   Wed, 18 Jan 2023 07:20:45 +0000
Message-ID: <PH0PR11MB5880C1B54DC57E31B6225147DAC79@PH0PR11MB5880.namprd11.prod.outlook.com>
References: <20230117074443.1982347-1-qiang1.zhang@intel.com>
 <Y8aql+vHNcdth0T1@lothringen>
In-Reply-To: <Y8aql+vHNcdth0T1@lothringen>
Accept-Language: en-US
Content-Language: en-US
x-ms-exchange-antispam-messagedata-chunkcount: 1
x-ms-exchange-antispam-messagedata-0: =?us-ascii?Q?gx+TbRJgAOPBrBbJA2AAIt7M6yBLoFhiuqqkxk69R9a/J7lSQOWqAGAnH5pI?=
 =?us-ascii?Q?ASyr6wjYd2E/QOIvvSUwyLuCqy44RrGreLU5ZNTpcrmn38MLaKcYtgLEHP44?=
 =?us-ascii?Q?UQ5pm5qoTuFTPO8W80iZcbCre8DtWuJiW3TLhK2FnwF6zYxRWorKYTYXBU56?=
 =?us-ascii?Q?vaaVo7b5rVnqnIOKRs7EPF4kXg091+PHAkYO9tjkyi3EMQlB0w/5zHjXUnWb?=
 =?us-ascii?Q?p9gOLv2YBNj6yBZv7mcnnD9CZTtJHZSYXjUal1FJm+CRe2BsPOUDTzhLzwgU?=
 =?us-ascii?Q?+ARUm+WLE21qd5liFaQnTALZ2YWSlQLuYTo4DzN9h/7tapKQzVLJqIZoln56?=
 =?us-ascii?Q?+OHyWlCVf/IP1229Xsfns5+IJozpKJ8E6IccR8ix7xnKPCR5zbIdqi/aZxnO?=
 =?us-ascii?Q?QzIVyUsDxCt1RW1VyEWF3z4llQpqk/P1ik+WAnf7Pco3gFQeme/gM954rZ0c?=
 =?us-ascii?Q?6iiv5HDLiyOTBwuXHx6nOfhup6gBacMItpEpEu9xodVkDeBm3C9L6oFZ7WTu?=
 =?us-ascii?Q?nkOsrlI6PcjTI++55ZOhTe96aREhpc/cHsJTwx7DWnjaq7bDIvlHM3ItcSzz?=
 =?us-ascii?Q?fIrKe9pwdWWqUn8Hcz3Mmg/PRVhbXeI8S/W8gYuj+aA6Wyj3hyNpJ9zGzh3t?=
 =?us-ascii?Q?Mb428H5CfTWanDU8pozfw/4EQ0GxpI8Mn2sFljA2BIVNKKMMgHbC9QEtuk8K?=
 =?us-ascii?Q?DbKP3GG8EZSqfROWP58e6jdmacrNbEm8VIAhKY46MJ8akdIKDYfnzDr2Md27?=
 =?us-ascii?Q?+zN+8ZYpxtrHS7jjqLOPzAOk8P1eAPTrWRYlykJAEl8pEqDdnzW1Kx7UPtpM?=
 =?us-ascii?Q?YfmiN6gH2i8MRclYIo4DDUjLIo24G0QIvsK9a1Tirf4I6n07PpPnChF6hPf1?=
 =?us-ascii?Q?h7Pb0EEze69YI9rF39EFu+PX/pRwQj4Gxl8IiFegvj5aCq66AKOeffB1piEK?=
 =?us-ascii?Q?N3wcgpM1Lj3JAVTB7NyBc/eYPgsm63QW2SoMOkdJtMOLrakQWQV0EHeLXIDa?=
 =?us-ascii?Q?+cHUJicbqSEVLh+bI8NbbHEJ3Wntwe0A9gqoPLBtFN0srjrUMalyG6W/AY/v?=
 =?us-ascii?Q?Sb92+KE/iQepwjxPfmR2pIqZzQrtkqqJoRic8bOdB1E/N79TZxgPjzp0lONa?=
 =?us-ascii?Q?1Obi7raDj0lBJPwALix+8GbBuOEyBoI+6bIwGS0rL8euG3Px+oCijdGlMj/L?=
 =?us-ascii?Q?Y9nLQJw/67VeaxoswLLmwgQTiQqThAlFVv622cv+s3wuW1NuZ7+YxNn3NBSx?=
 =?us-ascii?Q?N0bDEw6s4P3pmUVaWX2TVq7oYSj3ULp8FXS5knL2UG/Qa5WYglMnDNFizcn4?=
 =?us-ascii?Q?XAHmjFac8JDc543FUjZYoC3d6Rwhm0+LZKPhxL1AMuYptqNyp3yBXr1sMCIK?=
 =?us-ascii?Q?JWHo2gZLcCxOK/O1lNWuY2pCPnDnR3a0JMhBC+sdpW7KI8SCubN/kap4S/Uk?=
 =?us-ascii?Q?IweaGAahFozqFZGgN3vKlTFsPLmRzOB3qiCSHDE23G6cryLa9jhAcMzq/WS3?=
 =?us-ascii?Q?9MMZqumBMA5Qg75IJJK5P3Oozqa709Jt39n75eopAHUztwo6aHdBtlqyUIpZ?=
 =?us-ascii?Q?AXBl/ArxPMZ9jcMkYt7yI8NYHeeEz5It6PuT1AvC?=
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0
X-MS-Exchange-CrossTenant-AuthAs: Internal
X-MS-Exchange-CrossTenant-AuthSource: PH0PR11MB5880.namprd11.prod.outlook.com
X-MS-Exchange-CrossTenant-Network-Message-Id: da6b6547-7824-4641-7111-08daf9248420
X-MS-Exchange-CrossTenant-originalarrivaltime: 18 Jan 2023 07:20:45.6892
 (UTC)
X-MS-Exchange-CrossTenant-fromentityheader: Hosted
X-MS-Exchange-CrossTenant-id: 46c98d88-e344-4ed4-8496-4ed7712e255d
X-MS-Exchange-CrossTenant-mailboxtype: HOSTED
X-MS-Exchange-CrossTenant-userprincipalname: lmvrOZJNksS9kbGPjCQ/cPkx3wT+0R1PemRasa23Vk7vTluaC/Jc7/SwAxixR/q2xDB1FpvlmDrHmUuhQ1eCDA==
X-MS-Exchange-Transport-CrossTenantHeadersStamped: IA1PR11MB7174
X-OriginatorOrg: intel.com
X-Spam-Status: No, score=-4.4 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH,
        DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_MED,
        SPF_HELO_NONE,SPF_NONE autolearn=ham autolearn_force=no version=3.4.6
X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on
        lindbergh.monkeyblade.net
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Tue, Jan 17, 2023 at 03:44:43PM +0800, Zqiang wrote:
> When inovke rcu_report_qs_rdp(), if current CPU's rcu_data structure's ->
> grpmask has not been cleared from the corresponding rcu_node structure's
> ->qsmask, after that will clear and report quiescent state, but in this
> time, this also means that current grace period is not end, the current
> grace period is ongoing, because the rcu_gp_in_progress() currently retur=
n
> true, so for non-offloaded rdp, invoke rcu_accelerate_cbs() is impossible
> to return true.
>=20
> This commit therefore remove impossible rcu_gp_kthread_wake() calling.
>=20
> Signed-off-by: Zqiang <qiang1.zhang@intel.com>
> ---
>  kernel/rcu/tree.c | 5 +----
>  1 file changed, 1 insertion(+), 4 deletions(-)
>=20
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index b2c204529478..c78d48482583 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -1956,7 +1956,6 @@ rcu_report_qs_rdp(struct rcu_data *rdp)
>  {
>  	unsigned long flags;
>  	unsigned long mask;
> -	bool needwake =3D false;
>  	bool needacc =3D false;
>  	struct rcu_node *rnp;
> =20
> @@ -1988,7 +1987,7 @@ rcu_report_qs_rdp(struct rcu_data *rdp)
>  		 * NOCB kthreads have their own way to deal with that...
>  		 */
>  		if (!rcu_rdp_is_offloaded(rdp)) {
> -			needwake =3D rcu_accelerate_cbs(rnp, rdp);
> +			WARN_ON_ONCE(rcu_accelerate_cbs(rnp, rdp));
>
>Please also add a comment explaining why we don't expect to have
>to wake up the GP kthread.

Thanks Frederic, I will add comment next version.

>
>Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
>
>Thanks!
>

>  		} else if (!rcu_segcblist_completely_offloaded(&rdp->cblist)) {
>  			/*
>  			 * ...but NOCB kthreads may miss or delay callbacks acceleration
> @@ -2000,8 +1999,6 @@ rcu_report_qs_rdp(struct rcu_data *rdp)
>  		rcu_disable_urgency_upon_qs(rdp);
>  		rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
>  		/* ^^^ Released rnp->lock */
> -		if (needwake)
> -			rcu_gp_kthread_wake();
> =20
>  		if (needacc) {
>  			rcu_nocb_lock_irqsave(rdp, flags);
> --=20
> 2.25.1
>=20