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=-11.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_2 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 8F80AC433E1 for ; Thu, 13 Aug 2020 14:56:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6F13E20781 for ; Thu, 13 Aug 2020 14:56:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726699AbgHMO4s (ORCPT ); Thu, 13 Aug 2020 10:56:48 -0400 Received: from mail.kernel.org ([198.145.29.99]:49752 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726167AbgHMO4r (ORCPT ); Thu, 13 Aug 2020 10:56:47 -0400 Received: from oasis.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (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 15C2420781; Thu, 13 Aug 2020 14:56:46 +0000 (UTC) Date: Thu, 13 Aug 2020 10:56:44 -0400 From: Steven Rostedt To: Jiafei Pan Cc: "peterz@infradead.org" , "mingo@kernel.org" , "tglx@linutronix.de" , "romain.perier@gmail.com" , "will@kernel.org" , "linux-kernel@vger.kernel.org" , "linux-rt-users@vger.kernel.org" , Leo Li , Vladimir Oltean Subject: Re: [PATCH] softirq: add irq off checking for __raise_softirq_irqoff Message-ID: <20200813105644.1eb6f2cd@oasis.local.home> In-Reply-To: References: <20200806040729.39186-1-Jiafei.Pan@nxp.com> X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 13 Aug 2020 03:03:46 +0000 Jiafei Pan wrote: > Any comments? Thanks. > > @Steven Rostedt, I thinks irq off checking is necessary especially This is probably more for Thomas Gleixner. > for Preempt-RT kernel, because some context may be changed from irq > off to irq on when enable Preempt RT, I once met a issue that hrtimer > soft irq is lost when enabled Preempt RT, finally I found > napi_schedule_irqoff is called in hardware interrupt handler, there > maybe no issue for non RT kernel, but for Preempt RT, interrupt is > threaded, so irq is on in interrupt handler, the result is > __raise_softirq_irqoff is called in irq on context, so that per-CPU > softirq masking is corrupted because of the process of updating of > soft irq masking is interrupted and not a atomic operation , and then > caused hrtimer soft irq is lost. So I think adding irq status > checking in __raise_softirq_irqoff can report such issue directly and > help us to find the root cause of such issue. > > I know that there may be performance impaction to add extra checking > here, if it is the case, how about to include it in some debug > configuration items? Such as CONFIG_DEBUG_PREEMPT or other debug > items? > > Best Regards, > Jiafei. > > -----Original Message----- > From: Jiafei Pan > Sent: Thursday, August 6, 2020 12:07 PM > To: peterz@infradead.org; mingo@kernel.org; tglx@linutronix.de; rostedt@goodmis.org; romain.perier@gmail.com; will@kernel.org > Cc: linux-kernel@vger.kernel.org; linux-rt-users@vger.kernel.org; Jiafei Pan ; Leo Li ; Vladimir Oltean ; Jiafei Pan > Subject: [PATCH] softirq: add irq off checking for __raise_softirq_irqoff > > __raise_softirq_irqoff will update per-CPU mask of pending softirqs, it need to be called in irq disabled context in order to keep it atomic operation, otherwise it will be interrupted by hardware interrupt, and per-CPU softirqs pending mask will be corrupted, the result is there will be unexpected issue, for example hrtimer soft irq will be losed and soft hrtimer will never be expire and handled. Please wrap your change logs. > > Adding irqs disabled checking here to provide warning in irqs enabled context. > > Signed-off-by: Jiafei Pan > --- > kernel/softirq.c | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/kernel/softirq.c b/kernel/softirq.c index bf88d7f62433..11f61e54a3ae 100644 > --- a/kernel/softirq.c > +++ b/kernel/softirq.c > @@ -481,6 +481,11 @@ void raise_softirq(unsigned int nr) > > void __raise_softirq_irqoff(unsigned int nr) { > + /* This function can only be called in irq disabled context, > + * otherwise or_softirq_pending will be interrupted by hardware > + * interrupt, so that there will be unexpected issue. > + */ > + WARN_ON_ONCE(!irqs_disabled()); Perhaps: lockdep_assert_irqs_disabled() is more appropriate, and doesn't add extra overhead on production systems. -- Steve > trace_softirq_raise(nr); > or_softirq_pending(1UL << nr); > } > -- > 2.17.1