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 X-Spam-Level: X-Spam-Status: No, score=-7.5 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham 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 0AADBC04EBA for ; Thu, 29 Nov 2018 14:32:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CC3E72147C for ; Thu, 29 Nov 2018 14:32:22 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="UWgxLQ5i" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CC3E72147C Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linuxfoundation.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389433AbeK3Bhx (ORCPT ); Thu, 29 Nov 2018 20:37:53 -0500 Received: from mail.kernel.org ([198.145.29.99]:41082 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389406AbeK3Bhx (ORCPT ); Thu, 29 Nov 2018 20:37:53 -0500 Received: from localhost (5356596B.cm-6-7b.dynamic.ziggo.nl [83.86.89.107]) (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 6EAC4213A2; Thu, 29 Nov 2018 14:32:19 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1543501939; bh=5D2sBsUvpuB/Q/1VIDe3AlZhGTpt4RQHDLvvPIQwnEY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=UWgxLQ5icggkw0XN6vD/g6fQ5FcDbZksa9rkemnq+6RjKxrE7DS0zmjLxUb50s2tn QYsmB6ndB8ykX7Zj8XbRmr0Y0t0KwUqo8g1Q+cmEvKD/ybwCXmSzyM2Uy2IuumFLdP T8WSUR6SUiCCNvt77tITRzcGWOTtjGLEujb1SGtc= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Marius Hillenbrand , David Woodhouse , Peter Zijlstra , "Paul E. McKenney" Subject: [PATCH 4.19 104/110] rcu: Make need_resched() respond to urgent RCU-QS needs Date: Thu, 29 Nov 2018 15:13:15 +0100 Message-Id: <20181129135925.449820048@linuxfoundation.org> X-Mailer: git-send-email 2.19.2 In-Reply-To: <20181129135921.231283053@linuxfoundation.org> References: <20181129135921.231283053@linuxfoundation.org> User-Agent: quilt/0.65 X-stable: review MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 4.19-stable review patch. If anyone has any objections, please let me know. ------------------ From: Paul E. McKenney commit 92aa39e9dc77481b90cbef25e547d66cab901496 upstream. The per-CPU rcu_dynticks.rcu_urgent_qs variable communicates an urgent need for an RCU quiescent state from the force-quiescent-state processing within the grace-period kthread to context switches and to cond_resched(). Unfortunately, such urgent needs are not communicated to need_resched(), which is sometimes used to decide when to invoke cond_resched(), for but one example, within the KVM vcpu_run() function. As of v4.15, this can result in synchronize_sched() being delayed by up to ten seconds, which can be problematic, to say nothing of annoying. This commit therefore checks rcu_dynticks.rcu_urgent_qs from within rcu_check_callbacks(), which is invoked from the scheduling-clock interrupt handler. If the current task is not an idle task and is not executing in usermode, a context switch is forced, and either way, the rcu_dynticks.rcu_urgent_qs variable is set to false. If the current task is an idle task, then RCU's dyntick-idle code will detect the quiescent state, so no further action is required. Similarly, if the task is executing in usermode, other code in rcu_check_callbacks() and its called functions will report the corresponding quiescent state. Reported-by: Marius Hillenbrand Reported-by: David Woodhouse Suggested-by: Peter Zijlstra Signed-off-by: Paul E. McKenney [ paulmck: Backported to make patch apply cleanly on older versions. ] Tested-by: Marius Hillenbrand Cc: # 4.12.x - 4.19.x Signed-off-by: Greg Kroah-Hartman --- kernel/rcu/tree.c | 9 +++++++++ 1 file changed, 9 insertions(+) --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -2662,6 +2662,15 @@ void rcu_check_callbacks(int user) rcu_bh_qs(); } rcu_preempt_check_callbacks(); + /* The load-acquire pairs with the store-release setting to true. */ + if (smp_load_acquire(this_cpu_ptr(&rcu_dynticks.rcu_urgent_qs))) { + /* Idle and userspace execution already are quiescent states. */ + if (!rcu_is_cpu_rrupt_from_idle() && !user) { + set_tsk_need_resched(current); + set_preempt_need_resched(); + } + __this_cpu_write(rcu_dynticks.rcu_urgent_qs, false); + } if (rcu_pending()) invoke_rcu_core();