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=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_2 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 8E87EC34047 for ; Wed, 19 Feb 2020 15:51:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6C3B324677 for ; Wed, 19 Feb 2020 15:51:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726791AbgBSPvC (ORCPT ); Wed, 19 Feb 2020 10:51:02 -0500 Received: from mail.kernel.org ([198.145.29.99]:46448 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726569AbgBSPvB (ORCPT ); Wed, 19 Feb 2020 10:51:01 -0500 Received: from gandalf.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (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 BE58624671; Wed, 19 Feb 2020 15:50:59 +0000 (UTC) Date: Wed, 19 Feb 2020 10:50:58 -0500 From: Steven Rostedt To: Peter Zijlstra Cc: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, mingo@kernel.org, joel@joelfernandes.org, gregkh@linuxfoundation.org, gustavo@embeddedor.com, tglx@linutronix.de, paulmck@kernel.org, josh@joshtriplett.org, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com, luto@kernel.org, tony.luck@intel.com, frederic@kernel.org, dan.carpenter@oracle.com, mhiramat@kernel.org, "Steven Rostedt (VMware)" Subject: Re: [PATCH v3 09/22] sched,rcu,tracing: Avoid tracing before in_nmi() is correct Message-ID: <20200219105058.3b844e10@gandalf.local.home> In-Reply-To: <20200219150744.888917422@infradead.org> References: <20200219144724.800607165@infradead.org> <20200219150744.888917422@infradead.org> X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 19 Feb 2020 15:47:33 +0100 Peter Zijlstra wrote: > If we call into a tracer before in_nmi() becomes true, the tracer can > no longer detect it is called from NMI context and behave correctly. > > Therefore change nmi_{enter,exit}() to use __preempt_count_{add,sub}() > as the normal preempt_count_{add,sub}() have a (desired) function > trace entry. > > This fixes a potential issue with current code; AFAICT when the > function-tracer has stack-tracing enabled __trace_stack() will > malfunction when it hits the preempt_count_add() function entry from > NMI context. > > Suggested-by: Steven Rostedt (VMware) > Signed-off-by: Peter Zijlstra (Intel) > --- Reviewed-by: Steven Rostedt (VMware) -- Steve