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=-4.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,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 F1E08C10F13 for ; Sun, 14 Apr 2019 14:52:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C0A1720896 for ; Sun, 14 Apr 2019 14:52:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1555253566; bh=NxstMj+Bz/2ijvnCcxQWZ3/MSZ3aFE9+6Oz/hNYE5eA=; h=Date:From:To:Cc:Subject:In-Reply-To:References:List-ID:From; b=Swh8taxcGRBq5vcW1Yp9x33GyCR3MEXvfRF5PwpBjkdVJocPi1b5zOK99WQSowOgC mDU2kDUCNHv3tklMb490Ov3bme1o3jSmcNFZpS1FA5TUv7I2OCxvKF5xLtlodV6bYE UPh0fO/UUGP21LTQHqdBZkJZKnkY1Ww12fUema9w= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726531AbfDNOwp (ORCPT ); Sun, 14 Apr 2019 10:52:45 -0400 Received: from mail.kernel.org ([198.145.29.99]:58980 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726055AbfDNOwp (ORCPT ); Sun, 14 Apr 2019 10:52:45 -0400 Received: from devnote2 (NE2965lan1.rev.em-net.ne.jp [210.141.244.193]) (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 8520820684; Sun, 14 Apr 2019 14:52:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1555253563; bh=NxstMj+Bz/2ijvnCcxQWZ3/MSZ3aFE9+6Oz/hNYE5eA=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=bCY3FL5Jxe7dnxZ5Gejr1OvXMBZwdvwqv3cNgsQ3H1a4Brw8dwD0QYzWcRFtaxxG6 IHmAvaNa6EV+4tOpbTPf7f0oJSlGKqLAd/YMW0JUTLsacokYsZKFjSEzvyK3ueu3ME qCd++A/K1jB6s4/2RBqTgnAAeAum2mtadazBrFr4= Date: Sun, 14 Apr 2019 23:52:38 +0900 From: Masami Hiramatsu To: Russell King - ARM Linux admin Cc: Steven Rostedt , Stefan Agner , Arnd Bergmann , Masahiro Yamada , linux-arm-kernel@lists.infradead.org, naresh.kamboju@linaro.org, linux-kernel@vger.kernel.org Subject: Re: Kconfig dependency issue on function-graph tracer and frame pointer on arm Message-Id: <20190414235238.e860b1ce234752eff2b8c61c@kernel.org> In-Reply-To: <20190414133458.zxdekgx6qwd562qa@shell.armlinux.org.uk> References: <20190414194705.2e10802aca2df36c8f27f349@kernel.org> <20190414133458.zxdekgx6qwd562qa@shell.armlinux.org.uk> X-Mailer: Sylpheed 3.5.1 (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 Sun, 14 Apr 2019 14:34:58 +0100 Russell King - ARM Linux admin wrote: > On Sun, Apr 14, 2019 at 07:47:05PM +0900, Masami Hiramatsu wrote: > > Hello, > > > > Recently, Naresh reported that the function-graph tracer on the latest > > kernel crashes on arm. I could reproduce it and bisected. I finally found > > the commit f9b58e8c7d03 ("ARM: 8800/1: use choice for kernel unwinders") > > was the first bad commit. > > I don't think that littering the rest of the kernel Kconfig with ARM > specific stuff is really a viable solution to this. > > If we examine the current situation, we have: > > - THUMB2_KERNEL selecting ARM_UNWIND when enabled. > - UNWINDER_FRAME_POINTER disabled if THUMB2_KERNEL is enabled, provided > we're not using Clang. This leaves UNWINDER_ARM as the only choice, > which also selects ARM_UNWIND. > - The default choice is dependent on the settings of AEABI and > FUNCTION_GRAPH_TRACER. > - HAVE_FUNCTION_GRAPH_TRACER is disabled if THUMB2_KERNEL is enabled. > > which seems to be _way_ too messy. > > Looking back before this commit, the function graph tracer never had a > strong dependence on frame pointers being enabled in the kernel, but it > seems the code relies upon them (see ftrace_return_to_handler() in > kernel/trace/ and return_to_handler in arch/arm/kernel/entry-frace.S). > There is also the __ftrace_graph_caller macro which seems to rely on it. Yes, so I think similar bug is hiding in other LTS kernels. It should have a dependency to FRAME_POINTER on arm. > Since Clang does not support frame pointers, we shouldn't even offer > the function graph tracer for Clang compilers, so let's do that with > the first hunk of the patch below. > > The subsequent hunks remove the defaulting of the choice according to > the function graph tracer - this is not a "hint" where the user can > still choose either option irrespective of the state of the function > graph tracer. They should only be able to select the frame pointer > option in that case. Agreed. Using default for making dependency is wrong. > > Another way forward would be for someone to put the work in to making > the function graph tracer work without frame pointers. Yes, we eventually need that. But for fixing current released kernel (this bug is in v5.0 series), I think Kconfig fix is needed. > > So, how about this: > > diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig > index 850b4805e2d1..9aed25a6019b 100644 > --- a/arch/arm/Kconfig > +++ b/arch/arm/Kconfig > @@ -73,7 +73,7 @@ config ARM > select HAVE_EFFICIENT_UNALIGNED_ACCESS if (CPU_V6 || CPU_V6K || CPU_V7) && MMU > select HAVE_EXIT_THREAD > select HAVE_FTRACE_MCOUNT_RECORD if !XIP_KERNEL > - select HAVE_FUNCTION_GRAPH_TRACER if !THUMB2_KERNEL > + select HAVE_FUNCTION_GRAPH_TRACER if !THUMB2_KERNEL && !CC_IS_CLANG > select HAVE_FUNCTION_TRACER if !XIP_KERNEL > select HAVE_GCC_PLUGINS > select HAVE_HW_BREAKPOINT if PERF_EVENTS && (CPU_V6 || CPU_V6K || CPU_V7) > diff --git a/arch/arm/Kconfig.debug b/arch/arm/Kconfig.debug > index 6d6e0330930b..e388af4594a6 100644 > --- a/arch/arm/Kconfig.debug > +++ b/arch/arm/Kconfig.debug > @@ -47,8 +47,8 @@ config DEBUG_WX > > choice > prompt "Choose kernel unwinder" > - default UNWINDER_ARM if AEABI && !FUNCTION_GRAPH_TRACER > - default UNWINDER_FRAME_POINTER if !AEABI || FUNCTION_GRAPH_TRACER > + default UNWINDER_ARM if AEABI > + default UNWINDER_FRAME_POINTER if !AEABI If UNWINDER_ARM depends on ARM EABI, would we really need this "if !AEABI"? (I doubt we need these default...) > help > This determines which method will be used for unwinding kernel stack > traces for panics, oopses, bugs, warnings, perf, /proc//stack, > @@ -65,7 +65,7 @@ config UNWINDER_FRAME_POINTER > > config UNWINDER_ARM > bool "ARM EABI stack unwinder" > - depends on AEABI > + depends on AEABI && !FUNCTION_GRAPH_TRACER Hmm, AFAIK, FUNCTION_GRAPH_TRACER only depends on FRAME_POINTER, but not UNWINDER_FRAME_POINTER. So can user still choose UNWINDER_ARM even if FUNCTION_GRAPH_TRACER=y ? (Of course that may not be a meaningful option) Thank you, > select ARM_UNWIND > help > This option enables stack unwinding support in the kernel > > -- > RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ > FTTC broadband for 0.8mile line in suburbia: sync at 12.1Mbps down 622kbps up > According to speedtest.net: 11.9Mbps down 500kbps up -- Masami Hiramatsu