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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS 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 DA7A2C64E7A for ; Tue, 1 Dec 2020 14:56:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 633D32084C for ; Tue, 1 Dec 2020 14:56:06 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="IseEQmaT" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2391678AbgLAO4F (ORCPT ); Tue, 1 Dec 2020 09:56:05 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50170 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389514AbgLAO4F (ORCPT ); Tue, 1 Dec 2020 09:56:05 -0500 Received: from merlin.infradead.org (merlin.infradead.org [IPv6:2001:8b0:10b:1231::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id CDCE1C0613D6 for ; Tue, 1 Dec 2020 06:55:24 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=W1i0rg/foZpVr5SGX99+nlRzuL+ha07mtB+QnwQc4mw=; b=IseEQmaTDadFeYN0ipcC2DFqwP aLbriVSUHBQj1VXABEYKY3qv3jy2SPQmrhPwRBGEDWlyZLIsgxJUeaZAkg9Q2LiVJNxvo0C/L1RkL xZFfD8siiuivXUk8pQXIUNwQVkZZSyEuEzhijC7YOtcFjg7tgXd/jlGPBUTahewGCTIA7Dgt3Lm+e sb1sqvxR258s+zLRhpbuzxlmgYJ9HndxF3eqMujwX0eiGSXMkkSMCgPHmzL3ODPxk13LkMuuzj4fq l7+ZdNYxFkPDSuGJLK6hESmbx5dGGUl2M9VxUNYxhzYlpmfUxhYMP0DDJipDN3YiZMOcOVs/0Jbjk zVBnb4OA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1kk73o-0005kQ-JU; Tue, 01 Dec 2020 14:55:20 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 51904300DAE; Tue, 1 Dec 2020 15:55:19 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 3C46E2018E5AF; Tue, 1 Dec 2020 15:55:19 +0100 (CET) Date: Tue, 1 Dec 2020 15:55:19 +0100 From: Peter Zijlstra To: "Paul E. McKenney" 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: <20201201145519.GY2414@hirez.programming.kicks-ass.net> References: <20201130075651.GJ2414@hirez.programming.kicks-ass.net> <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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201201144644.GF1437@paulmck-ThinkPad-P72> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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.