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=-10.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,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 F2C01C43603 for ; Tue, 10 Dec 2019 04:26:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C8F1420652 for ; Tue, 10 Dec 2019 04:26:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1575952009; bh=nGo2kmgXIxoagRTq8l20EvB15yLGsqGpyLAdga1D6qw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=oG/vtshJGcNSntv1aBm9ESqAVGP7cEDQ80G6tWXOoEw5dEpPUI94Gg0rZYtU9LX51 GsVSVA3mwbcOQGdbbWsCrBjA89zkmYvEZGnsZGvZRzwp4w1Mz8VKBK0dAiOxiGys6C f/8rIf/MTcteV3iAlDid6PVxZAjMdORGwQezO1qg= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727194AbfLJE0n (ORCPT ); Mon, 9 Dec 2019 23:26:43 -0500 Received: from mail.kernel.org ([198.145.29.99]:48766 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727047AbfLJE0j (ORCPT ); Mon, 9 Dec 2019 23:26:39 -0500 Received: from paulmck-ThinkPad-P72.home (199-192-87-166.static.wiline.com [199.192.87.166]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 8573524655; Tue, 10 Dec 2019 04:26:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1575951999; bh=nGo2kmgXIxoagRTq8l20EvB15yLGsqGpyLAdga1D6qw=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=QTupLXawxvHRe+E6B1i1MuklKexXcPE6KHn0gCFE/yM4+ztBGT54oZmqw/aNn/oP6 vRtYscRB/81ss4h5PD9W4HdXxw9I4zso2Mgekvr2+RrvfiMGRxWsLk3wsna6h88PoE oT8TgR+KmEoHr0CLRTKIS6Yhvit93397lN1mosx8= From: paulmck@kernel.org To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com, mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org, "Paul E. McKenney" Subject: [PATCH tip/core/rcu 11/11] rcu: Avoid tick_dep_set_cpu() misordering Date: Mon, 9 Dec 2019 20:26:29 -0800 Message-Id: <20191210042629.3808-11-paulmck@kernel.org> X-Mailer: git-send-email 2.9.5 In-Reply-To: <20191210042606.GA3624@paulmck-ThinkPad-P72> References: <20191210042606.GA3624@paulmck-ThinkPad-P72> Sender: rcu-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org From: "Paul E. McKenney" In the current code, rcu_nmi_enter_common() might decide to turn on the tick using tick_dep_set_cpu(), but be delayed just before doing so. Then the grace-period kthread might notice that the CPU in question had in fact gone through a quiescent state, thus turning off the tick using tick_dep_clear_cpu(). The later invocation of tick_dep_set_cpu() would then incorrectly leave the tick on. This commit therefore enlists the aid of the leaf rcu_node structure's ->lock to ensure that decisions to enable or disable the tick are carried out before they can be reversed. Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 5445da2..b0e0612 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -800,8 +800,8 @@ void rcu_user_exit(void) */ static __always_inline void rcu_nmi_enter_common(bool irq) { - struct rcu_data *rdp = this_cpu_ptr(&rcu_data); long incby = 2; + struct rcu_data *rdp = this_cpu_ptr(&rcu_data); /* Complain about underflow. */ WARN_ON_ONCE(rdp->dynticks_nmi_nesting < 0); @@ -828,8 +828,13 @@ static __always_inline void rcu_nmi_enter_common(bool irq) } else if (tick_nohz_full_cpu(rdp->cpu) && rdp->dynticks_nmi_nesting == DYNTICK_IRQ_NONIDLE && READ_ONCE(rdp->rcu_urgent_qs) && !rdp->rcu_forced_tick) { - rdp->rcu_forced_tick = true; - tick_dep_set_cpu(rdp->cpu, TICK_DEP_BIT_RCU); + raw_spin_lock_rcu_node(rdp->mynode); + // Recheck under lock. + if (rdp->rcu_urgent_qs && !rdp->rcu_forced_tick) { + rdp->rcu_forced_tick = true; + tick_dep_set_cpu(rdp->cpu, TICK_DEP_BIT_RCU); + } + raw_spin_unlock_rcu_node(rdp->mynode); } trace_rcu_dyntick(incby == 1 ? TPS("Endirq") : TPS("++="), rdp->dynticks_nmi_nesting, @@ -898,6 +903,7 @@ void rcu_irq_enter_irqson(void) */ static void rcu_disable_urgency_upon_qs(struct rcu_data *rdp) { + raw_lockdep_assert_held_rcu_node(rdp->mynode); WRITE_ONCE(rdp->rcu_urgent_qs, false); WRITE_ONCE(rdp->rcu_need_heavy_qs, false); if (tick_nohz_full_cpu(rdp->cpu) && rdp->rcu_forced_tick) { -- 2.9.5