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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED, USER_AGENT_MUTT 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 308F1C0044C for ; Thu, 1 Nov 2018 23:16:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C9C9120820 for ; Thu, 1 Nov 2018 23:16:25 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C9C9120820 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.ibm.com 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 S1728111AbeKBIVY (ORCPT ); Fri, 2 Nov 2018 04:21:24 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:53758 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728053AbeKBIVY (ORCPT ); Fri, 2 Nov 2018 04:21:24 -0400 Received: from pps.filterd (m0098413.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.22/8.16.0.22) with SMTP id wA1NDm5q121119 for ; Thu, 1 Nov 2018 19:16:21 -0400 Received: from e17.ny.us.ibm.com (e17.ny.us.ibm.com [129.33.205.207]) by mx0b-001b2d01.pphosted.com with ESMTP id 2ng8vrmsj9-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Thu, 01 Nov 2018 19:16:21 -0400 Received: from localhost by e17.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 1 Nov 2018 23:16:21 -0000 Received: from b01cxnp22036.gho.pok.ibm.com (9.57.198.26) by e17.ny.us.ibm.com (146.89.104.204) with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Thu, 1 Nov 2018 23:16:18 -0000 Received: from b01ledav003.gho.pok.ibm.com (b01ledav003.gho.pok.ibm.com [9.57.199.108]) by b01cxnp22036.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id wA1NGHMO33226842 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=FAIL); Thu, 1 Nov 2018 23:16:17 GMT Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 70643B205F; Thu, 1 Nov 2018 23:16:17 +0000 (GMT) Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 3F3EFB2064; Thu, 1 Nov 2018 23:16:17 +0000 (GMT) Received: from paulmck-ThinkPad-W541 (unknown [9.70.82.141]) by b01ledav003.gho.pok.ibm.com (Postfix) with ESMTP; Thu, 1 Nov 2018 23:16:17 +0000 (GMT) Received: by paulmck-ThinkPad-W541 (Postfix, from userid 1000) id C373916C34AA; Thu, 1 Nov 2018 16:16:17 -0700 (PDT) Date: Thu, 1 Nov 2018 16:16:17 -0700 From: "Paul E. McKenney" To: tglx@linutronix.de, bigeasy@linutronix.de Cc: linux-rt-users@vger.kernel.org, linux-kernel@vger.kernel.org Subject: rcu: Make ksoftirqd do RCU quiescent states Reply-To: paulmck@linux.ibm.com MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 18110123-0040-0000-0000-0000048B0779 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00009968; HX=3.00000242; KW=3.00000007; PH=3.00000004; SC=3.00000268; SDB=6.01111303; UDB=6.00575898; IPR=6.00891394; MB=3.00023997; MTD=3.00000008; XFM=3.00000015; UTC=2018-11-01 23:16:19 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18110123-0041-0000-0000-00000894085E Message-Id: <20181101231617.GA10882@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:,, definitions=2018-11-01_16:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=741 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1807170000 definitions=main-1811010193 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > Implementing RCU-bh in terms of RCU-preempt makes the system vulnerable > to network-based denial-of-service attacks. This patch therefore > makes __do_softirq() invoke rcu_bh_qs(), but only when __do_softirq() > is running in ksoftirqd context. A wrapper layer in interposed so that > other calls to __do_softirq() avoid invoking rcu_bh_qs(). The underlying > function __do_softirq_common() does the actual work. > > The reason that rcu_bh_qs() is bad in these non-ksoftirqd contexts is > that there might be a local_bh_enable() inside an RCU-preempt read-side > critical section. This local_bh_enable() can invoke __do_softirq() > directly, so if __do_softirq() were to invoke rcu_bh_qs() (which just > calls rcu_preempt_qs() in the PREEMPT_RT_FULL case), there would be > an illegal RCU-preempt quiescent state in the middle of an RCU-preempt > read-side critical section. Therefore, quiescent states can only happen > in cases where __do_softirq() is invoked directly from ksoftirqd. I -think- that the need for this goes away in the current merge window because RCU-bh is going away. There might still be an rt-specific need to disable irqs, though. Thanx, Paul > Signed-off-by: Paul E. McKenney > Link: http://lkml.kernel.org/r/20111005184518.GA21601@linux.vnet.ibm.com > Signed-off-by: Thomas Gleixner > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > index 197088cdb56e..968579b86401 100644 > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -244,7 +244,19 @@ void rcu_sched_qs(void) > this_cpu_ptr(&rcu_sched_data), true); > } > > -#ifndef CONFIG_PREEMPT_RT_FULL > +#ifdef CONFIG_PREEMPT_RT_FULL > +static void rcu_preempt_qs(void); > + > +void rcu_bh_qs(void) > +{ > + unsigned long flags; > + > + /* Callers to this function, rcu_preempt_qs(), must disable irqs. */ > + local_irq_save(flags); > + rcu_preempt_qs(); > + local_irq_restore(flags); > +} > +#else > void rcu_bh_qs(void) > { > RCU_LOCKDEP_WARN(preemptible(), "rcu_bh_qs() invoked with preemption enabled!!!"); > diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h > index 429a2f144e19..bee9bffeb0ce 100644 > --- a/kernel/rcu/tree_plugin.h > +++ b/kernel/rcu/tree_plugin.h > @@ -29,6 +29,7 @@ > #include > #include > #include > +#include > #include > #include > #include "../time/tick-internal.h" > @@ -1407,7 +1408,7 @@ static void rcu_prepare_kthreads(int cpu) > > #endif /* #else #ifdef CONFIG_RCU_BOOST */ > > -#if !defined(CONFIG_RCU_FAST_NO_HZ) > +#if !defined(CONFIG_RCU_FAST_NO_HZ) || defined(CONFIG_PREEMPT_RT_FULL) > > /* > * Check to see if any future RCU-related work will need to be done > @@ -1423,7 +1424,9 @@ int rcu_needs_cpu(u64 basemono, u64 *nextevt) > *nextevt = KTIME_MAX; > return rcu_cpu_has_callbacks(NULL); > } > +#endif /* !defined(CONFIG_RCU_FAST_NO_HZ) || defined(CONFIG_PREEMPT_RT_FULL) */ > > +#if !defined(CONFIG_RCU_FAST_NO_HZ) > /* > * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up > * after it. > @@ -1520,6 +1523,8 @@ static bool __maybe_unused rcu_try_advance_all_cbs(void) > return cbs_ready; > } > > +#ifndef CONFIG_PREEMPT_RT_FULL > + > /* > * Allow the CPU to enter dyntick-idle mode unless it has callbacks ready > * to invoke. If the CPU has callbacks, try to advance them. Tell the > @@ -1562,6 +1567,7 @@ int rcu_needs_cpu(u64 basemono, u64 *nextevt) > *nextevt = basemono + dj * TICK_NSEC; > return 0; > } > +#endif /* #ifndef CONFIG_PREEMPT_RT_FULL */ > > /* > * Prepare a CPU for idle from an RCU perspective. The first major task