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=-12.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 C2C6EC433E0 for ; Mon, 22 Feb 2021 21:33:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 724AD64E02 for ; Mon, 22 Feb 2021 21:33:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232070AbhBVVdE (ORCPT ); Mon, 22 Feb 2021 16:33:04 -0500 Received: from mail.kernel.org ([198.145.29.99]:38138 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230483AbhBVVcl (ORCPT ); Mon, 22 Feb 2021 16:32:41 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id BAE1764E02; Mon, 22 Feb 2021 21:32:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1614029520; bh=Eh42XbJyyXC24A1STrMBcBWCKsBVxzw5KXWISRssFgw=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=jIvQRbWAKTXaCs3OS46GAMEyEsHVHm3FZZ8YHfFZlN6ny1X9d7iTt+uZfQ7iQ3zhq WLiuK902y2pUaXwxWcRX2naFYAa9WIGYMDUWXarYCB6DWUIh9r9MmVAfKSdudPZAxC gF5nx4hMamhVVZJzQO18Jrxli3xAYFvrJacWVBl276KgpdCjL75BUksZpZia1lR1a1 kkCk65p9uPLrWt2x8gQjDui3YsM0BoKt901LJws8mItigaGnWbn4nYTJwEqHb8EkED qfmgJR51OJIr1mhZ/PdA/D+NBspeA4FUn5QNkIeppGWpWB7+Zvl+bLxwjcY6QTwF3+ QwoEoqLYpWMkQ== Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id 74D2B35227D5; Mon, 22 Feb 2021 13:32:00 -0800 (PST) Date: Mon, 22 Feb 2021 13:32:00 -0800 From: "Paul E. McKenney" To: Uladzislau Rezki Cc: Sebastian Andrzej Siewior , Masami Hiramatsu , Ingo Molnar , Steven Rostedt , Peter Zijlstra , Thomas Gleixner , LKML , RCU , Michael Ellerman , Andrew Morton , Daniel Axtens , Frederic Weisbecker , Neeraj Upadhyay , Joel Fernandes , Michal Hocko , "Theodore Y . Ts'o" , Oleksiy Avramchenko Subject: Re: [PATCH] kprobes: Fix to delay the kprobes jump optimization Message-ID: <20210222213200.GN2743@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20210219112357.GA34462@pc638.lan> <20210219112751.GA34528@pc638.lan> <20210219181811.GY2743@paulmck-ThinkPad-P72> <20210219183336.GA23049@paulmck-ThinkPad-P72> <20210222102104.v3pr7t57hmpwijpi@linutronix.de> <20210222125431.GA41939@pc638.lan> <20210222150903.GH2743@paulmck-ThinkPad-P72> <20210222171605.GA42169@pc638.lan> <20210222181608.GK2743@paulmck-ThinkPad-P72> <20210222190703.GA19167@pc638.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20210222190703.GA19167@pc638.lan> User-Agent: Mutt/1.9.4 (2018-02-28) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 22, 2021 at 08:07:03PM +0100, Uladzislau Rezki wrote: > On Mon, Feb 22, 2021 at 10:16:08AM -0800, Paul E. McKenney wrote: > > On Mon, Feb 22, 2021 at 06:16:05PM +0100, Uladzislau Rezki wrote: > > > On Mon, Feb 22, 2021 at 07:09:03AM -0800, Paul E. McKenney wrote: > > > > On Mon, Feb 22, 2021 at 01:54:31PM +0100, Uladzislau Rezki wrote: > > > > > On Mon, Feb 22, 2021 at 11:21:04AM +0100, Sebastian Andrzej Siewior wrote: > > > > > > On 2021-02-19 10:33:36 [-0800], Paul E. McKenney wrote: > > > > > > > For definiteness, here is the first part of the change, posted earlier. > > > > > > > The commit log needs to be updated. I will post the change that keeps > > > > > > > the tick going as a reply to this email. > > > > > > … > > > > > > > diff --git a/kernel/softirq.c b/kernel/softirq.c > > > > > > > index 9d71046..ba78e63 100644 > > > > > > > --- a/kernel/softirq.c > > > > > > > +++ b/kernel/softirq.c > > > > > > > @@ -209,7 +209,7 @@ static inline void invoke_softirq(void) > > > > > > > if (ksoftirqd_running(local_softirq_pending())) > > > > > > > return; > > > > > > > > > > > > > > - if (!force_irqthreads) { > > > > > > > + if (!force_irqthreads || !__this_cpu_read(ksoftirqd)) { > > > > > > > #ifdef CONFIG_HAVE_IRQ_EXIT_ON_IRQ_STACK > > > > > > > /* > > > > > > > * We can safely execute softirq on the current stack if > > > > > > > @@ -358,8 +358,8 @@ asmlinkage __visible void __softirq_entry __do_softirq(void) > > > > > > > > > > > > > > pending = local_softirq_pending(); > > > > > > > if (pending) { > > > > > > > - if (time_before(jiffies, end) && !need_resched() && > > > > > > > - --max_restart) > > > > > > > + if (!__this_cpu_read(ksoftirqd) || > > > > > > > + (time_before(jiffies, end) && !need_resched() && --max_restart)) > > > > > > > goto restart; > > > > > > > > > > > > This is hunk shouldn't be needed. The reason for it is probably that the > > > > > > following wakeup_softirqd() would avoid further invoke_softirq() > > > > > > performing the actual softirq work. It would leave early due to > > > > > > ksoftirqd_running(). Unless I'm wrong, any raise_softirq() invocation > > > > > > outside of an interrupt would do the same. > > > > > > > > And it does pass the rcutorture test without that hunk: > > > > > > > > tools/testing/selftests/rcutorture/bin/kvm.sh --allcpus --duration 2 --configs "TREE03" --kconfig "CONFIG_DEBUG_LOCK_ALLOC=y CONFIG_PROVE_LOCKING=y" --bootargs "threadirqs=1" --trust-make > > > > > > > Yep. I have tested that patch also. It works for me as well. So > > > technically i do not see any issues from the first glance but of > > > course it should be reviewed by the softirq people to hear their > > > opinion. > > > > > > IRQs are enabled, so it can be handled from an IRQ tail until > > > ksoftirqd threads are spawned. > > > > And if I add "CONFIG_NO_HZ_IDLE=y CONFIG_HZ_PERIODIC=n" it still works, > > even if I revert my changes to rcu_needs_cpu(). Should I rely on this > > working globally? ;-) > > > There might be corner cases which we are not aware of so far. From the > other hand what the patch does is simulating the !threadirqs behaviour > during early boot. In that case we know that handling of SW irqs from > real-irq tail works :) Sold! I keep the rcu_needs_cpu() changes, just in case. Thanx, Paul