From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:41516 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752731AbdJLXKr (ORCPT ); Thu, 12 Oct 2017 19:10:47 -0400 Received: from pps.filterd (m0098399.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.21/8.16.0.21) with SMTP id v9CNAemw085351 for ; Thu, 12 Oct 2017 19:10:47 -0400 Received: from e18.ny.us.ibm.com (e18.ny.us.ibm.com [129.33.205.208]) by mx0a-001b2d01.pphosted.com with ESMTP id 2djfnacat1-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Thu, 12 Oct 2017 19:10:44 -0400 Received: from localhost by e18.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Thu, 12 Oct 2017 19:09:30 -0400 Date: Thu, 12 Oct 2017 16:09:28 -0700 From: "Paul E. McKenney" To: stable@vger.kernel.org Cc: gregkh@linuxfoundation.org, rostedt@goodmis.org Subject: [PATCH -stable] rcu: Allow for page faults in NMI handlers Reply-To: paulmck@linux.vnet.ibm.com MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Message-Id: <20171012230928.GA31473@linux.vnet.ibm.com> Sender: stable-owner@vger.kernel.org List-ID: A number of architecture invoke rcu_irq_enter() on exception entry in order to allow RCU read-side critical sections in the exception handler when the exception is from an idle or nohz_full CPU. This works, at least unless the exception happens in an NMI handler. In that case, rcu_nmi_enter() would already have exited the extended quiescent state, which would mean that rcu_irq_enter() would (incorrectly) cause RCU to think that it is again in an extended quiescent state. This will in turn result in lockdep splats in response to later RCU read-side critical sections. This commit therefore causes rcu_irq_enter() and rcu_irq_exit() to take no action if there is an rcu_nmi_enter() in effect, thus avoiding the unscheduled return to RCU quiescent state. This in turn should make the kernel safe for on-demand RCU voyeurism. Link: http://lkml.kernel.org/r/20170922211022.GA18084@linux.vnet.ibm.com Cc: stable@vger.kernel.org # 4.2.x Fixes: 0be964be0 ("module: Sanitize RCU usage and locking") Reported-by: Steven Rostedt Signed-off-by: Paul E. McKenney Signed-off-by: Steven Rostedt (VMware) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index f07343b54fe5..8a62cbfe1f2f 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -759,6 +759,12 @@ void rcu_irq_exit(void) local_irq_save(flags); rdtp = this_cpu_ptr(&rcu_dynticks); + + /* Page faults can happen in NMI handlers, so check... */ + if (READ_ONCE(rdtp->dynticks_nmi_nesting)) + return; + + RCU_LOCKDEP_WARN(!irqs_disabled(), "rcu_irq_exit() invoked with irqs enabled!!!"); oldval = rdtp->dynticks_nesting; rdtp->dynticks_nesting--; WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && @@ -887,6 +893,12 @@ void rcu_irq_enter(void) local_irq_save(flags); rdtp = this_cpu_ptr(&rcu_dynticks); + + /* Page faults can happen in NMI handlers, so check... */ + if (READ_ONCE(rdtp->dynticks_nmi_nesting)) + return; + + RCU_LOCKDEP_WARN(!irqs_disabled(), "rcu_irq_enter() invoked with irqs enabled!!!"); oldval = rdtp->dynticks_nesting; rdtp->dynticks_nesting++; WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&