From patchwork Tue Oct 27 13:50:53 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg Kroah-Hartman X-Patchwork-Id: 312238 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-12.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH, MAILING_LIST_MULTI, SIGNED_OFF_BY, SPF_HELO_NONE, SPF_PASS, URIBL_BLOCKED, USER_AGENT_GIT autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 425BFC388F9 for ; Tue, 27 Oct 2020 16:46:34 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D434322263 for ; Tue, 27 Oct 2020 16:46:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603817193; bh=j8sycDWh7wTs5cS/7e+OSsDH8CYam9rdxktbp1y7oco=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=0psoYDNln2alUC3cS92+SDrk0F6hKostUurnz2H0Jwcva2QywZU4Q0cUiugTOutAx oknJVoo3wGoGakqUzRvDwRGioIdJvsEpqkjKM12avDDghajK+7dJ7dJf7MIAGE2Huw mfp9KU4P8jTbmcwuX9tjnyug63TU/cEHtwwk+dfA= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1799474AbgJ0Pm1 (ORCPT ); Tue, 27 Oct 2020 11:42:27 -0400 Received: from mail.kernel.org ([198.145.29.99]:55596 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1800592AbgJ0Pgp (ORCPT ); Tue, 27 Oct 2020 11:36:45 -0400 Received: from localhost (83-86-74-64.cable.dynamic.v4.ziggo.nl [83.86.74.64]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 56E372064B; Tue, 27 Oct 2020 15:36:42 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603813003; bh=j8sycDWh7wTs5cS/7e+OSsDH8CYam9rdxktbp1y7oco=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=i3p3LokKp8beafogzL0nOvYdLK3fCzOQUpCv/1hLXYPN+WvfmnQrfmt9R+pDVMLq6 uwzqlUC38Llf8JTbO1N2z/AjhFiWnmJbb63GPZq1cwfYc2OXediTof0GQoSykNY2Ru szXtIVR4zr1YIYT3CE2JAQ2TFmhFnuua0Up/KXak= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, "Joel Fernandes (Google)" , Neeraj Upadhyay , "Paul E. McKenney" , Sasha Levin Subject: [PATCH 5.9 403/757] rcu/tree: Force quiescent state on callback overload Date: Tue, 27 Oct 2020 14:50:53 +0100 Message-Id: <20201027135509.484474750@linuxfoundation.org> X-Mailer: git-send-email 2.29.1 In-Reply-To: <20201027135450.497324313@linuxfoundation.org> References: <20201027135450.497324313@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Neeraj Upadhyay [ Upstream commit 9c39245382de4d52a122641952900709d4a9950b ] On callback overload, it is necessary to quickly detect idle CPUs, and rcu_gp_fqs_check_wake() checks for this condition. Unfortunately, the code following the call to this function does not repeat this check, which means that in reality no actual quiescent-state forcing, instead only a couple of quick and pointless wakeups at the beginning of the grace period. This commit therefore adds a check for the RCU_GP_FLAG_OVLD flag in the post-wakeup "if" statement in rcu_gp_fqs_loop(). Fixes: 1fca4d12f4637 ("rcu: Expedite first two FQS scans under callback-overload conditions") Reviewed-by: Joel Fernandes (Google) Signed-off-by: Neeraj Upadhyay Signed-off-by: Paul E. McKenney Signed-off-by: Sasha Levin --- kernel/rcu/tree.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index f78ee759af9cb..388a2ad292bf4 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -1898,7 +1898,7 @@ static void rcu_gp_fqs_loop(void) break; /* If time for quiescent-state forcing, do it. */ if (!time_after(rcu_state.jiffies_force_qs, jiffies) || - (gf & RCU_GP_FLAG_FQS)) { + (gf & (RCU_GP_FLAG_FQS | RCU_GP_FLAG_OVLD))) { trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("fqsstart")); rcu_gp_fqs(first_gp_fqs);