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=-7.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 476B2C433DB for ; Fri, 19 Feb 2021 20:05:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 148C064EB7 for ; Fri, 19 Feb 2021 20:05:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230053AbhBSUEv (ORCPT ); Fri, 19 Feb 2021 15:04:51 -0500 Received: from mail.kernel.org ([198.145.29.99]:34062 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229515AbhBSUEs (ORCPT ); Fri, 19 Feb 2021 15:04:48 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 8DA9E64EAF; Fri, 19 Feb 2021 20:04:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1613765047; bh=Zlci/AmdKj0FlBYDWFBN2+f3PZab3/D9d+nTODN6EFA=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=Y7Z3/p7LBPRUIx0+KnL8gQEeNW60J4AxXN08vWXeRabAfn7bgCNn4U8Hl9c0Vn2i8 Y9Q0AZ6I66evTtzNwD1RDKzz3Nt5DuDAPquJlgpymDMFxBPR3g7npnL75l1N69zS0M gcCt1JFvgodYUMcDg8EC9t8N51Zg5XdWzbOdWXB+5xfApoMehsQ9Jqd1+WBOgitSaY YjiKd8Q+DcmYcjrjpzMjBr9drmsz04E1QIuGsn3Myg9xaoNyA68DrddNb/OrrHTHWy Xfc1dUbv2mVLMsNcaihcpH+W6871y7o0D6NcEwSaWVkC28/dEp/jKMCGdAoPTuTHUv LElUZIG9jjt1w== Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id 3834F3520E6A; Fri, 19 Feb 2021 12:04:07 -0800 (PST) Date: Fri, 19 Feb 2021 12:04:07 -0800 From: "Paul E. McKenney" To: Steven Rostedt Cc: Uladzislau Rezki , Sebastian Andrzej Siewior , Masami Hiramatsu , Ingo Molnar , 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: <20210219200407.GA18400@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20210219081755.eucq4srbam6wg2gm@linutronix.de> <20210219104958.GA34308@pc638.lan> <20210219105710.d626zexj6vzt6k6y@linutronix.de> <20210219111301.GA34441@pc638.lan> <20210219111738.go6i2fdzvavpotxd@linutronix.de> <20210219112357.GA34462@pc638.lan> <20210219112751.GA34528@pc638.lan> <20210219181811.GY2743@paulmck-ThinkPad-P72> <20210219141429.53def012@gandalf.local.home> <20210219194539.GZ2743@paulmck-ThinkPad-P72> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210219194539.GZ2743@paulmck-ThinkPad-P72> User-Agent: Mutt/1.9.4 (2018-02-28) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Feb 19, 2021 at 11:45:39AM -0800, Paul E. McKenney wrote: > On Fri, Feb 19, 2021 at 02:14:29PM -0500, Steven Rostedt wrote: > > On Fri, 19 Feb 2021 10:18:11 -0800 > > "Paul E. McKenney" wrote: > > > > > We can further prevent entry into dyntick-idle state until > > > the ksoftirqd kthreads have been spawned, which means that if softirq > > > handlers must be deferred, they will be resumed within one jiffy by the > > > next scheduler-clock interrupt. > > > > Why not just prevent entry into dyntick-idle state until the system is > > finished booting? As you said; There should be no latency-sensitive > > applications running, until after we started the system. > > Exactly, and that is the effect of patch to rcu_needs_cpu() that I just > now posted. > > Ah, your point is that if the tick keeps running, there is no need to > modify softirq? Good point, and I will test that, thank you!!! But sadly keeping the tick on without also modifying softirq still results in a hang. The problem is that when the kernel is booted with threadirqs=1, invoke_softirq() will avoid ever running the softirq handlers on the backside of an interrupt. So is this where Sebastian tells me that some -rt transformation can result in locking-based deadlocks if softirq handlers are ever run on the backside of an interrupt? ;-) Thanx, Paul