From mboxrd@z Thu Jan 1 00:00:00 1970 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 765EBC61DA4 for ; Wed, 15 Mar 2023 19:45:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232694AbjCOTpU (ORCPT ); Wed, 15 Mar 2023 15:45:20 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47712 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232654AbjCOToq (ORCPT ); Wed, 15 Mar 2023 15:44:46 -0400 Received: from mail-qt1-x82b.google.com (mail-qt1-x82b.google.com [IPv6:2607:f8b0:4864:20::82b]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B389D199FE for ; Wed, 15 Mar 2023 12:44:34 -0700 (PDT) Received: by mail-qt1-x82b.google.com with SMTP id r16so17474515qtx.9 for ; Wed, 15 Mar 2023 12:44:34 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=joelfernandes.org; s=google; t=1678909473; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=ThU1XJtO1aLExHCNuOZtJgSY8HbvsH7BE8/boByrYno=; b=ag5X7WW6rfx5+7t1/eBsvLbRkB0y7Vb/fHHyhSxrRthTHHyDI7UjKzwlHHipX9cFtF Kka1hk8oKQDU69luA4VDWIBakHNnDiGrOW8TUl6Tbt1TJYOVUHXpB2E2TdW5uov5uc98 nrZnUhAVT3BLC9hxVe2eeMxuyFGzvMETCnPyU= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; t=1678909473; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=ThU1XJtO1aLExHCNuOZtJgSY8HbvsH7BE8/boByrYno=; b=Fhj64vxTzuqChlK/ZrFgvhjtaqqTVSs8WPcvFkwztxAQ/0BW/QPYOJ6mpabmJuExkB jbQNvuOiM6LxGvhj+8NiXC1+7dRfVcNn4w8bvlXSwo1Q9CbVq8EBqFKQA4pD1VbrldJF gPNnrMDEP8YCkNW6EyjsImHDMgrAgDpo6KCoHmZhBno8h1TKS7Esy+O6xBUH2hjYT5Vs aLUbgUe9EWwEKYSxLLpCCIC8kenus+5fNckJYf1Qvue8GwRrRoAOAjDIPo5zYP2Il5EV QjbpXqSuOHEGuOTAK8Q439XA37tnAVxk1GTc3IwsMY2bu9JAGVtrtPyAy3tZU1/VeOov CdNQ== X-Gm-Message-State: AO0yUKWZdzk2HagI5bEy8a+2AF2mwGdrN1/5hBkvXhHcobLxSUaWWhvP oZcN2OJBK9ygB3t8AUKq7KQE/1AwVqXdgoPsjzQ= X-Google-Smtp-Source: AK7set9eHeATCHiRK0lgFQHYvnJM3VGTCsQZJTXU87E+PPKBbb5RQF3SZBaL8sWIrBT9HAPSQX7+ug== X-Received: by 2002:a05:622a:1902:b0:3b6:93fe:443c with SMTP id w2-20020a05622a190200b003b693fe443cmr1567792qtc.32.1678909473597; Wed, 15 Mar 2023 12:44:33 -0700 (PDT) Received: from joelboxx.c.googlers.com.com (129.239.188.35.bc.googleusercontent.com. [35.188.239.129]) by smtp.gmail.com with ESMTPSA id c15-20020ac8660f000000b003b86b088755sm4346666qtp.15.2023.03.15.12.44.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 15 Mar 2023 12:44:33 -0700 (PDT) From: "Joel Fernandes (Google)" To: linux-kernel@vger.kernel.org, "Paul E. McKenney" , Frederic Weisbecker , Neeraj Upadhyay , Josh Triplett , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Joel Fernandes Cc: Zqiang , rcu@vger.kernel.org Subject: [PATCH 5/9] rcu: Remove never-set needwake assignment from rcu_report_qs_rdp() Date: Wed, 15 Mar 2023 19:43:45 +0000 Message-Id: <20230315194349.10798-5-joel@joelfernandes.org> X-Mailer: git-send-email 2.40.0.rc1.284.g88254d51c5-goog In-Reply-To: <20230315194349.10798-1-joel@joelfernandes.org> References: <20230315194349.10798-1-joel@joelfernandes.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Zqiang The rcu_accelerate_cbs() function is invoked by rcu_report_qs_rdp() only if there is a grace period in progress that is still blocked by at least one CPU on this rcu_node structure. This means that rcu_accelerate_cbs() should never return the value true, and thus that this function should never set the needwake variable and in turn never invoke rcu_gp_kthread_wake(). This commit therefore removes the needwake variable and the invocation of rcu_gp_kthread_wake() in favor of a WARN_ON_ONCE() on the call to rcu_accelerate_cbs(). The purpose of this new WARN_ON_ONCE() is to detect situations where the system's opinion differs from ours. Signed-off-by: Zqiang Reviewed-by: Frederic Weisbecker Signed-off-by: Paul E. McKenney Signed-off-by: Joel Fernandes (Google) --- kernel/rcu/tree.c | 10 ++++++---- 1 file changed, 6 insertions(+), 4 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 8e880c09ab59..e80e8f128c57 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -1955,7 +1955,6 @@ rcu_report_qs_rdp(struct rcu_data *rdp) { unsigned long flags; unsigned long mask; - bool needwake = false; bool needacc = false; struct rcu_node *rnp; @@ -1987,7 +1986,12 @@ 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 = rcu_accelerate_cbs(rnp, rdp); + /* + * The current GP has not yet ended, so it + * should not be possible for rcu_accelerate_cbs() + * to return true. So complain, but don't awaken. + */ + WARN_ON_ONCE(rcu_accelerate_cbs(rnp, rdp)); } else if (!rcu_segcblist_completely_offloaded(&rdp->cblist)) { /* * ...but NOCB kthreads may miss or delay callbacks acceleration @@ -1999,8 +2003,6 @@ 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(); if (needacc) { rcu_nocb_lock_irqsave(rdp, flags); -- 2.40.0.rc1.284.g88254d51c5-goog