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=-9.0 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=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 9B685C64E7A for ; Tue, 1 Dec 2020 16:54:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 19FCB208C3 for ; Tue, 1 Dec 2020 16:54:15 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="sA7nWhnq" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390983AbgLAQyD (ORCPT ); Tue, 1 Dec 2020 11:54:03 -0500 Received: from mail.kernel.org ([198.145.29.99]:38324 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390913AbgLAQyC (ORCPT ); Tue, 1 Dec 2020 11:54:02 -0500 Received: from paulmck-ThinkPad-P72.home (50-39-104-11.bvtn.or.frontiernet.net [50.39.104.11]) (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 9499C2076C; Tue, 1 Dec 2020 16:53:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1606841601; bh=TEWdhOtpWAceOHta5XtZgvrih2TxouGP6j2ld6oWDIA=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=sA7nWhnq1J9mvA2xnC0pCu/QajRgdODor0lroauRGA3A9kzUqOYldlp6VBONWMeGm ZR9QL3ffnTKMI3lUnPfnElSwZvf6uf/cw8M922XOCfc4mKgpnNHNuWjpX3Q3ubiLIe /s5SIXH5Rm/G7CJxDWMcP/Gm0VFcCOXwO28Dq7Zg= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id 2FCBD35225C2; Tue, 1 Dec 2020 08:53:21 -0800 (PST) Date: Tue, 1 Dec 2020 08:53:21 -0800 From: "Paul E. McKenney" To: Peter Zijlstra Cc: Christian Borntraeger , Linus Torvalds , Sven Schnelle , Thomas Gleixner , Linux Kernel Mailing List , the arch/x86 maintainers Subject: Re: [GIT pull] locking/urgent for v5.10-rc6 Message-ID: <20201201165321.GG1437@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20201130125211.GN2414@hirez.programming.kicks-ass.net> <20201130130315.GJ3092@hirez.programming.kicks-ass.net> <20201201080734.GQ2414@hirez.programming.kicks-ass.net> <20201201110724.GL3092@hirez.programming.kicks-ass.net> <20201201144644.GF1437@paulmck-ThinkPad-P72> <20201201145519.GY2414@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201201145519.GY2414@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.9.4 (2018-02-28) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Dec 01, 2020 at 03:55:19PM +0100, Peter Zijlstra wrote: > On Tue, Dec 01, 2020 at 06:46:44AM -0800, Paul E. McKenney wrote: > > > > So after having talked to Sven a bit, the thing that is happening, is > > > that this is the one place where we take interrupts with RCU being > > > disabled. Normally RCU is watching and all is well, except during idle. > > > > Isn't interrupt entry supposed to invoke rcu_irq_enter() at some point? > > Or did this fall victim to recent optimizations? > > It does, but the problem is that s390 is still using > trace_hardirqs_off(), which calls into tracing before RCU is enabled. > > The entry order between lockdep, rcu and tracing is critical. > > You can't call into tracing without RCU running, > you can't call into RCU without lockdep setup, > you can't call the (old) lockdep setup without landing in tracing. Whew! ;-) Thanx, Paul