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=-6.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_PASS,URIBL_BLOCKED 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 D7200C32789 for ; Sun, 4 Nov 2018 14:32:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8E0F52082E for ; Sun, 4 Nov 2018 14:32:44 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="Ve/3FBK6" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8E0F52082E Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.com 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 S1729818AbeKDXrz (ORCPT ); Sun, 4 Nov 2018 18:47:55 -0500 Received: from mail-it1-f194.google.com ([209.85.166.194]:34298 "EHLO mail-it1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727834AbeKDXrz (ORCPT ); Sun, 4 Nov 2018 18:47:55 -0500 Received: by mail-it1-f194.google.com with SMTP id t189-v6so5496200itf.1 for ; Sun, 04 Nov 2018 06:32:42 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=mTqncDFkWSPxrkfWfS+PVBK3VTvu8+moWor7mB98kcI=; b=Ve/3FBK6Ng6Bbx5p7qIhb/4gr4mLD8nSy4mk5U1020SQiyXTAx9/Gv0H0Pg84/8Kfn Wfy1pg7DnkJ1fhwiXLD58+NgI8eADdd6YuEvD+kU6sAFOzSTdA3X+9y682kZGUaRTRfM 7n1/KhIRUspPVx1QW6Hh9q6IvizAukkkrdqAnkIppERmK3aFEdVqrvPLVp9qME6VtmG9 OCAmEOLHsipbnbu3i19OlZpT8TZZkfICNqom3Sz4N3qG9HXNEq7tAa/VHuq+sBeCKyIq WmSIS9NMfbPzIv2ww4c+wgXu/s47NnEIXqtv2F9xj66v3hysgrm46IqudB3RcnSXiw25 IP/A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=mTqncDFkWSPxrkfWfS+PVBK3VTvu8+moWor7mB98kcI=; b=QQZ10w+eYo6qjzsqDvu8gYJfqXikJcBynzPKB2PJqNYtpp1YV/QtUgYszj8SAAQSJm rT3sVO6v8toWzC0scLeJO1GMoVsD6ELAQzMdn7scPSb3nk1FHWyLPcIEmrFiwrcyNfSw yEHkM8k3FSKUDxV1v9Q4n3aGWqRLGtJZ7df5VhRNWRjvzB11Ct9tzfALDv/u+AdMXkMG FLv80FMXzGndc6VmbFijHEM/s/oXOWgIj4yZhR5CpB4EL2C+eSAt+KQO331x4z9WLpms BQ0it7QvHD30thyCppO9QUKof0kGuIsrMExQXlPrT6ePwvgb2kZqLm7r6EKNdc6Yr21C HbrQ== X-Gm-Message-State: AGRZ1gLzfd3VX4hj2Hn0MeZIAte41g6b1n989mksV8v3+3X063aDGBeY iY/Wshgs9/30W4hWU8/nXs/Z9nw4MHg3VipMyiF+LJoAE9uM/g== X-Google-Smtp-Source: AJdET5e0UQClkd/dfVlpPfnhN4FdUVfva7ORlWcQJXfLhdAMXSZzi2PCOh1yXiCSjyZzoBYhg3hRL+t7rXujSLgjd7A= X-Received: by 2002:a02:9b46:: with SMTP id g6-v6mr17208708jal.60.1541341961778; Sun, 04 Nov 2018 06:32:41 -0800 (PST) MIME-Version: 1.0 References: <20181104023537.2626-1-tiny.windzz@gmail.com> <20181104090649.7c206915@vmware.local.home> In-Reply-To: <20181104090649.7c206915@vmware.local.home> From: Frank Lee Date: Sun, 4 Nov 2018 22:32:27 +0800 Message-ID: Subject: Re: [PATCH] tracing/fgraph: remove unnecessary unlikely() To: rostedt@goodmis.org Cc: mingo@kernel.org, linux-kernel@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Sorry for this place, I should consider this situation. -- Yangtao On Sun, Nov 4, 2018 at 10:06 PM Steven Rostedt wrote: > > On Sat, 3 Nov 2018 22:35:37 -0400 > Yangtao Li wrote: > > > WARN_ON() already contains an unlikely(), so it's not necessary to use > > unlikely. > > NACK... see below. > > > > > Signed-off-by: Yangtao Li > > --- > > kernel/trace/trace_functions_graph.c | 6 ++---- > > 1 file changed, 2 insertions(+), 4 deletions(-) > > > > diff --git a/kernel/trace/trace_functions_graph.c b/kernel/trace/trace_functions_graph.c > > index 169b3c44ee97..f8c2a08e4985 100644 > > --- a/kernel/trace/trace_functions_graph.c > > +++ b/kernel/trace/trace_functions_graph.c > > @@ -201,9 +201,8 @@ ftrace_pop_return_trace(struct ftrace_graph_ret *trace, unsigned long *ret, > > if (index < 0) > > index += FTRACE_NOTRACE_DEPTH; > > > > - if (unlikely(index < 0 || index >= FTRACE_RETFUNC_DEPTH)) { > > + if (WARN_ON(index < 0 || index >= FTRACE_RETFUNC_DEPTH)) { > > When function graph is enabled, the printk from the warn on will likely > be traced as well and trigger the same WARN_ON, which will again cause > a recursion loop and crash and reboot the box with no output at all. > > > ftrace_graph_stop(); > > Notice that I call ftrace_graph_stop() *before* the WARN_ON(). This > disables the ftrace graph tracer and prevents the recursion loop from > happening. > > There's a reason that the WARN_ON() is placed where it is. > > But thanks for the report, it shows that I need to add a comment here > so that someone else doesn't send a similar patch in the future. > > -- Steve > > > > - WARN_ON(1); > > /* Might as well panic, otherwise we have no where to go */ > > *ret = (unsigned long)panic; > > return; > > @@ -274,9 +273,8 @@ unsigned long ftrace_return_to_handler(unsigned long frame_pointer) > > */ > > ftrace_graph_return(&trace); > > > > - if (unlikely(!ret)) { > > + if (WARN_ON(!ret)) { > > ftrace_graph_stop(); > > - WARN_ON(1); > > /* Might as well panic. What else to do? */ > > ret = (unsigned long)panic; > > } >