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=-9.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, 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 9B593C19759 for ; Thu, 1 Aug 2019 22:33:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 76BF6206B8 for ; Thu, 1 Aug 2019 22:33:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387737AbfHAWdA (ORCPT ); Thu, 1 Aug 2019 18:33:00 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:9398 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1733064AbfHAWdA (ORCPT ); Thu, 1 Aug 2019 18:33:00 -0400 Received: from pps.filterd (m0098396.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.27/8.16.0.27) with SMTP id x71MWFFH114015; Thu, 1 Aug 2019 18:32:19 -0400 Received: from pps.reinject (localhost [127.0.0.1]) by mx0a-001b2d01.pphosted.com with ESMTP id 2u475rumjt-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 01 Aug 2019 18:32:19 -0400 Received: from m0098396.ppops.net (m0098396.ppops.net [127.0.0.1]) by pps.reinject (8.16.0.27/8.16.0.27) with SMTP id x71MWIDe114326; Thu, 1 Aug 2019 18:32:19 -0400 Received: from ppma05wdc.us.ibm.com (1b.90.2fa9.ip4.static.sl-reverse.com [169.47.144.27]) by mx0a-001b2d01.pphosted.com with ESMTP id 2u475rumbv-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 01 Aug 2019 18:32:18 -0400 Received: from pps.filterd (ppma05wdc.us.ibm.com [127.0.0.1]) by ppma05wdc.us.ibm.com (8.16.0.27/8.16.0.27) with SMTP id x71MV1sM021427; Thu, 1 Aug 2019 22:31:59 GMT Received: from b01cxnp23034.gho.pok.ibm.com (b01cxnp23034.gho.pok.ibm.com [9.57.198.29]) by ppma05wdc.us.ibm.com with ESMTP id 2u0e85w6dk-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Thu, 01 Aug 2019 22:31:59 +0000 Received: from b01ledav003.gho.pok.ibm.com (b01ledav003.gho.pok.ibm.com [9.57.199.108]) by b01cxnp23034.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x71MVwFI50528540 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 1 Aug 2019 22:31:58 GMT Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 5F872B205F; Thu, 1 Aug 2019 22:31:58 +0000 (GMT) Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 4A33DB2067; Thu, 1 Aug 2019 22:31:58 +0000 (GMT) Received: from paulmck-ThinkPad-W541 (unknown [9.70.82.154]) by b01ledav003.gho.pok.ibm.com (Postfix) with ESMTP; Thu, 1 Aug 2019 22:31:58 +0000 (GMT) Received: by paulmck-ThinkPad-W541 (Postfix, from userid 1000) id 9FFF616C9A39; Thu, 1 Aug 2019 15:31:59 -0700 (PDT) From: "Paul E. McKenney" To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, 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 1/3] rcu: Simplify rcu_read_unlock_special() deferred wakeups Date: Thu, 1 Aug 2019 15:31:56 -0700 Message-Id: <20190801223158.14407-1-paulmck@linux.ibm.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20190801223132.GA14044@linux.ibm.com> References: <20190801223132.GA14044@linux.ibm.com> X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2019-08-01_09:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=13 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1906280000 definitions=main-1908010237 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org In !use_softirq runs, we clearly cannot rely on raise_softirq() and its lightweight bit setting, so we must instead do some form of wakeup. In the absence of a self-IPI when interrupts are disabled, these wakeups can be delayed until the next interrupt occurs. This means that calling invoke_rcu_core() doesn't actually do any expediting. In this case, it is better to take the "else" clause, which sets the current CPU's resched bits and, if there is an expedited grace period in flight, uses IRQ-work to force the needed self-IPI. This commit therefore removes the "else if" clause that calls invoke_rcu_core(). Reported-by: Scott Wood Signed-off-by: Paul E. McKenney --- kernel/rcu/tree_plugin.h | 7 +------ 1 file changed, 1 insertion(+), 6 deletions(-) diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index acb225023ed1..3f0701e860e4 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -631,17 +631,12 @@ static void rcu_read_unlock_special(struct task_struct *t) // Using softirq, safe to awaken, and we get // no help from enabling irqs, unlike bh/preempt. raise_softirq_irqoff(RCU_SOFTIRQ); - } else if (exp && irqs_were_disabled && !use_softirq && - !t->rcu_read_unlock_special.b.deferred_qs) { - // Safe to awaken and we get no help from enabling - // irqs, unlike bh/preempt. - invoke_rcu_core(); } else { // Enabling BH or preempt does reschedule, so... // Also if no expediting or NO_HZ_FULL, slow is OK. set_tsk_need_resched(current); set_preempt_need_resched(); - if (IS_ENABLED(CONFIG_IRQ_WORK) && + if (IS_ENABLED(CONFIG_IRQ_WORK) && irqs_were_disabled && !rdp->defer_qs_iw_pending && exp) { // Get scheduler to re-evaluate and call hooks. // If !IRQ_WORK, FQS scan will eventually IPI. -- 2.17.1