From nobody Tue Sep 16 10:55:50 2025 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id BB2B3C54EBD for ; Thu, 5 Jan 2023 00:34:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S240496AbjAEAeL (ORCPT ); Wed, 4 Jan 2023 19:34:11 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:41220 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S240379AbjAEAdZ (ORCPT ); Wed, 4 Jan 2023 19:33:25 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id AD18A4FCEA; Wed, 4 Jan 2023 16:28:59 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 7EF65B81988; Thu, 5 Jan 2023 00:28:56 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id DF2C5C433A7; Thu, 5 Jan 2023 00:28:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1672878534; bh=heNZkRhselcUeK4W6Q42S6IveI27Tt7taSP/M5NwFFM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Aba7WF8cgEF1Bwy6JU335bbMuWtqY3kl6l+V6sgmq18nrg5LiMEAGf0ytUrKsC80z BULDrr7tdKY/1k/j+HVxKUHqCLymrjgjj5z9IvzbdUbQHfV2oXBLg+EzbnFYS32ogr ME2+z1VycL+DkZgkkbhrIcr2AZGPf/ig49v7KBmGJMwbuvvO6QYNORK8jwQGcIGM47 QctrgyXeUmXZ18/t3FiQLJHy6TU7NQ4crkv2Oc5IiEPGwpU7v7ib5e6pawql4+pbI0 gDVP3m9ZUlaV0oMgrdqczD2nIJIrcD3OzekcHRrH6q/cwVvtcUuT8QV+azfyu/iauM UQL+hHLZLxfYQ== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 50C745C1AE0; Wed, 4 Jan 2023 16:28:54 -0800 (PST) From: "Paul E. McKenney" To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@meta.com, rostedt@goodmis.org, Pingfan Liu , Lai Jiangshan , Frederic Weisbecker , Josh Triplett , Mathieu Desnoyers , "Paul E . McKenney" Subject: [PATCH rcu 7/9] srcu: Remove needless rcu_seq_done() check while holding read lock Date: Wed, 4 Jan 2023 16:28:51 -0800 Message-Id: <20230105002853.1769401-7-paulmck@kernel.org> X-Mailer: git-send-email 2.31.1.189.g2e36527f23 In-Reply-To: <20230105002845.GA1769240@paulmck-ThinkPad-P17-Gen-1> References: <20230105002845.GA1769240@paulmck-ThinkPad-P17-Gen-1> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" From: Pingfan Liu The srcu_gp_start_if_needed() function now read-holds the srcu_struct whose grace period is being started, which means that the corresponding SRCU grace period cannot end. This in turn means that the SRCU grace-period sequence number returned by rcu_seq_snap() cannot expire during this time. And that means that the calls to rcu_seq_done() in srcu_funnel_exp_start() and srcu_funnel_gp_start() can never return true. This commit therefore removes these rcu_seq_done() checks, but adds checks in kernels built with CONFIG_PROVE_RCU=3Dy that splats if rcu_seq_done() does somehow return true. [ paulmck: Rearrange checks to handle kernels built with lockdep. ] Signed-off-by: Pingfan Liu Cc: Lai Jiangshan Cc: Frederic Weisbecker Cc: Josh Triplett Cc: Steven Rostedt Cc: Mathieu Desnoyers To: rcu@vger.kernel.org Signed-off-by: Paul E. McKenney --- kernel/rcu/srcutree.c | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-) diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index 6af0312005801..68b8d8b150db1 100644 --- a/kernel/rcu/srcutree.c +++ b/kernel/rcu/srcutree.c @@ -915,7 +915,7 @@ static void srcu_funnel_exp_start(struct srcu_struct *s= sp, struct srcu_node *snp if (snp) for (; snp !=3D NULL; snp =3D snp->srcu_parent) { sgsne =3D READ_ONCE(snp->srcu_gp_seq_needed_exp); - if (rcu_seq_done(&ssp->srcu_gp_seq, s) || + if (WARN_ON_ONCE(rcu_seq_done(&ssp->srcu_gp_seq, s)) || (!srcu_invl_snp_seq(sgsne) && ULONG_CMP_GE(sgsne, s))) return; spin_lock_irqsave_rcu_node(snp, flags); @@ -942,6 +942,9 @@ static void srcu_funnel_exp_start(struct srcu_struct *s= sp, struct srcu_node *snp * * Note that this function also does the work of srcu_funnel_exp_start(), * in some cases by directly invoking it. + * + * The srcu read lock should be hold around this function. And s is a seq = snap + * after holding that lock. */ static void srcu_funnel_gp_start(struct srcu_struct *ssp, struct srcu_data= *sdp, unsigned long s, bool do_norm) @@ -962,7 +965,7 @@ static void srcu_funnel_gp_start(struct srcu_struct *ss= p, struct srcu_data *sdp, if (snp_leaf) /* Each pass through the loop does one level of the srcu_node tree. */ for (snp =3D snp_leaf; snp !=3D NULL; snp =3D snp->srcu_parent) { - if (rcu_seq_done(&ssp->srcu_gp_seq, s) && snp !=3D snp_leaf) + if (WARN_ON_ONCE(rcu_seq_done(&ssp->srcu_gp_seq, s)) && snp !=3D snp_le= af) return; /* GP already done and CBs recorded. */ spin_lock_irqsave_rcu_node(snp, flags); snp_seq =3D snp->srcu_have_cbs[idx]; @@ -999,8 +1002,8 @@ static void srcu_funnel_gp_start(struct srcu_struct *s= sp, struct srcu_data *sdp, if (!do_norm && ULONG_CMP_LT(ssp->srcu_gp_seq_needed_exp, s)) WRITE_ONCE(ssp->srcu_gp_seq_needed_exp, s); =20 - /* If grace period not already done and none in progress, start it. */ - if (!rcu_seq_done(&ssp->srcu_gp_seq, s) && + /* If grace period not already in progress, start it. */ + if (!WARN_ON_ONCE(rcu_seq_done(&ssp->srcu_gp_seq, s)) && rcu_seq_state(ssp->srcu_gp_seq) =3D=3D SRCU_STATE_IDLE) { WARN_ON_ONCE(ULONG_CMP_GE(ssp->srcu_gp_seq, ssp->srcu_gp_seq_needed)); srcu_gp_start(ssp); --=20 2.31.1.189.g2e36527f23