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=-5.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,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 E23EFC7618B for ; Mon, 29 Jul 2019 10:30:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B226D2075C for ; Mon, 29 Jul 2019 10:30:07 +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="yWdcwTjF" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728243AbfG2KaG (ORCPT ); Mon, 29 Jul 2019 06:30:06 -0400 Received: from merlin.infradead.org ([205.233.59.134]:45162 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728030AbfG2KaG (ORCPT ); Mon, 29 Jul 2019 06:30:06 -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=gjj4owKXS61+aOLcK4Kpf98oFWq8xT7RivisxYBZ5eE=; b=yWdcwTjFmfouyg41jH87v9pQg IctmrGHLJJw3D9Z3kKe4hUw299hYfgiWUmyqhAuJ9rqQwYaRfpZPOdSV8LofaIfrPTHa5Fd9+wzue +wzccYlNHT2xaP2HTCOWBY4w56DwZktDofxkSrE2A5E2LRcUE9VuMBIypjQHrk+3JJSI+AUBg62k4 C+j6W+phAOPG+gpQJghzzmomdqSzmIxJI7eMpNEVHTAzz3xVrp/iU6ugBE4NBMafuGnzT5AdQvABq NmZ3egFiflgBB7P+pxU0O5W51W8bCR6EKbKMMVfZ/uoi6WHUF5azuQStAvXM+TZtFEz+NddYNV4AI LRmkaTSCg==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92 #3 (Red Hat Linux)) id 1hs2uc-0000eV-0C; Mon, 29 Jul 2019 10:29:50 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 52ACB20AF2C34; Mon, 29 Jul 2019 12:29:48 +0200 (CEST) Date: Mon, 29 Jul 2019 12:29:48 +0200 From: Peter Zijlstra To: Andy Lutomirski Cc: Eiichi Tsukata , Joel Fernandes , "Paul E. McKenney" , Thomas Gleixner , Steven Rostedt , Ingo Molnar , Frederic Weisbecker , LKML Subject: Re: [PATCH] tracing: Prevent RCU EQS breakage in preemptirq events Message-ID: <20190729102948.GY31381@hirez.programming.kicks-ass.net> References: <20190729010734.3352-1-devel@etsukata.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Jul 28, 2019 at 09:25:58PM -0700, Andy Lutomirski wrote: > On Sun, Jul 28, 2019 at 6:08 PM Eiichi Tsukata wrote: > > diff --git a/kernel/trace/trace_preemptirq.c b/kernel/trace/trace_preemptirq.c > > index 4d8e99fdbbbe..031b51cb94d0 100644 > > --- a/kernel/trace/trace_preemptirq.c > > +++ b/kernel/trace/trace_preemptirq.c > > @@ -10,6 +10,7 @@ > > #include > > #include > > #include > > +#include > > #include "trace.h" > > > > #define CREATE_TRACE_POINTS > > @@ -49,9 +50,14 @@ NOKPROBE_SYMBOL(trace_hardirqs_off); > > > > __visible void trace_hardirqs_on_caller(unsigned long caller_addr) > > { > > + enum ctx_state prev_state; > > + > > if (this_cpu_read(tracing_irq_cpu)) { > > - if (!in_nmi()) > > + if (!in_nmi()) { > > + prev_state = exception_enter(); > > trace_irq_enable_rcuidle(CALLER_ADDR0, caller_addr); > > + exception_exit(prev_state); > > + } > > tracer_hardirqs_on(CALLER_ADDR0, caller_addr); > > this_cpu_write(tracing_irq_cpu, 0); > > } > > This seems a bit distressing. Now we're going to do a whole bunch of > context tracking transitions for each kernel entry. Would a better > fix me to change trace_hardirqs_on_caller to skip the trace event if > the previous state was already IRQs on and, more importantly, to skip > tracing IRQs off if IRQs were already off? The x86 code is very > careful to avoid ever having IRQs on and CONTEXT_USER at the same > time. I think they already (try to) do that; see 'tracing_irq_cpu'.