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=-2.1 required=3.0 tests=DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,T_DKIM_INVALID, USER_AGENT_MUTT 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 0B286C4321E for ; Fri, 7 Sep 2018 07:35:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B6B0E2075E for ; Fri, 7 Sep 2018 07:35:00 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="v005ubu5" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B6B0E2075E Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727791AbeIGMOg (ORCPT ); Fri, 7 Sep 2018 08:14:36 -0400 Received: from merlin.infradead.org ([205.233.59.134]:52754 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725942AbeIGMOf (ORCPT ); Fri, 7 Sep 2018 08:14:35 -0400 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:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=6AQiD9D2levhriXbeDepjyHN/nm3dK7vD8VzK4LogX0=; b=v005ubu5lP//KQK5nMFrrIxfx dc9Nd+FKLyFROyz8sjHtQV+nYHwt9MygVpoINVkrVcKDS1Ug0JAAY0PeJMLADbApUN3TTqW+pln2J Gwak9/LlTSgqTiyjUHAmxAEtsIXtDN7GrR+TqwH1eC6mwPIFeP1tkFIuLqCHWvbADAg3gJGDHT/lP jhDZySEy2DXHRuKtoaKYm3lGONotABXksU3LCsFvq9HepVuh2Ufx+SmK2IdxZEdZ7x4TtMt7TQAuP FnLkBmqwrYM8jKnhGRQyqdiJyi+V26WokuHD/D2CEyl0lTPay6HQPSly29MnigwGZ1wQrAptIoInr W1YMueKdA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1fyBI3-0007h0-93; Fri, 07 Sep 2018 07:34:51 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 04F39201F9C52; Fri, 7 Sep 2018 09:34:49 +0200 (CEST) Date: Fri, 7 Sep 2018 09:34:48 +0200 From: Peter Zijlstra To: Steven Rostedt Cc: LKML , Ingo Molnar , Thomas Gleixner , Petr Mladek , Sergey Senozhatsky , "Paul E. McKenney" Subject: Re: [PATCH] printk/tracing: Do not trace printk_nmi_enter() Message-ID: <20180907073448.GL24106@hirez.programming.kicks-ass.net> References: <20180905213334.03375777@vmware.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180905213334.03375777@vmware.local.home> User-Agent: Mutt/1.10.0 (2018-05-17) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Sep 05, 2018 at 09:33:34PM -0400, Steven Rostedt wrote: > do_idle { > > [interrupts enabled] > > [interrupts disabled] > TRACE_IRQS_OFF [lockdep says irqs off] > [...] > TRACE_IRQS_IRET > test if pt_regs say return to interrupts enabled [yes] > TRACE_IRQS_ON [lockdep says irqs are on] > > > nmi_enter() { > printk_nmi_enter() [traced by ftrace] > [ hit ftrace breakpoint ] > > TRACE_IRQS_OFF [lockdep says irqs off] > [...] > TRACE_IRQS_IRET [return from breakpoint] > test if pt_regs say interrupts enabled [no] > [iret back to interrupt] > [iret back to code] > > tick_nohz_idle_enter() { > > lockdep_assert_irqs_enabled() [lockdep say no!] Isn't the problem that we muck with the IRQ state from NMI context? We shouldn't be doing that. The thing is, since we trace the IRQ state from within IRQ-disable, since that's the only IRQ-safe option, it is very much not NMI-safe. Your patch might avoid the symptom, but I don't think it cures the fundamental problem.