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=-7.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_PASS 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 81019C43441 for ; Mon, 26 Nov 2018 05:16:07 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3BBF52086B for ; Mon, 26 Nov 2018 05:16:07 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="wdCIpjH0" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3BBF52086B Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.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 S1726252AbeKZQI7 (ORCPT ); Mon, 26 Nov 2018 11:08:59 -0500 Received: from mail.kernel.org ([198.145.29.99]:53252 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726144AbeKZQI6 (ORCPT ); Mon, 26 Nov 2018 11:08:58 -0500 Received: from devnote (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 95AA120660; Mon, 26 Nov 2018 05:15:59 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1543209362; bh=58GUl73SmHSM3NX9bHWiLDrWqwW+HlxuAcXmspvUsGk=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=wdCIpjH0me2URW3lcxXBtkH0xV9B1uE0IaCW0hS8L0r5J8i/Iz1BRXs1oHYDbqLbQ TDa0RZy77ySfXp/y3O6WXlwI+/xY2f73UckR8pn/H9uji5KGT/v5ridN9gbDXXUqlJ xkAj2f05gf4eqXMEkSN+GI0HBxg/+FHq6ECNccJU= Date: Mon, 26 Nov 2018 14:15:57 +0900 From: Masami Hiramatsu To: Steven Rostedt Cc: linux-kernel@vger.kernel.org, Linus Torvalds , Ingo Molnar , Andrew Morton , Thomas Gleixner , Peter Zijlstra , linux-arch@vger.kernel.org, Joel Fernandes , Masami Hiramatsu , Josh Poimboeuf , Andy Lutomirski , Frederic Weisbecker Subject: Re: [for-next][PATCH 00/18] function_graph: Add separate depth counter to prevent trace corruption Message-Id: <20181126141557.3f7be1aad456345b9a0dfcae@kernel.org> In-Reply-To: <20181122002801.501220343@goodmis.org> References: <20181122002801.501220343@goodmis.org> X-Mailer: Sylpheed 3.5.0 (GTK+ 2.24.30; 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 Hi Steve, This series looks good to me. Reviewed-by: Masami Hiramatsu for this series. Thank you! # Now I know why sometimes func-graph depth looks broken... On Wed, 21 Nov 2018 19:28:01 -0500 Steven Rostedt wrote: > While working on rewriting function graph tracer, I found a design > flaw in the code. Commit 03274a3ffb449 ("tracing/fgraph: Adjust fgraph depth > before calling trace return callback") tried to fix a bug that caused > interrupts not to be traced if max_depth was set to 1 (for debugging > NO_HZ_FULL), because if it came in just as another function that was being > traced that had a depth of 1 was exiting. This caused the timing of being in > the kernel to be off. The fix was simply to move the calling of the return > function after the updating of curr_ret_stack index as that was what was > being used. > > The change log even says that it was safe to do this, but unfortunately it > was not, and the barrier() there was specifically *for* that function (which > shows why one should document barriers). > > The problem is that the return callback may still be using what's on the > shadow stack and by changing the shadow stack pointer, it may allow for > another function being traced to overwrite that data. Note, if this happens, > it will only cause garbage data to be traced and will not affect the actual > operations of the kernel (ie. it wont crash). > > Unfortunately just reverting that will bring back the old bug. The real way > to fix that old bug is to create another counter to handle the depth, but > this means that we need to change all the architectures that implement > function graph tracing (that's 12 of them). Luckily, I need to do this > anyway in my re-design so this is a good thing. > > Since all the archictectures do basicall the same thing to prepare the > function graph trace to be traced, I made a generic function that they all > can use and simplified the logic of all the architectures. Then I'm able to > fix the design problem in one place. > > I pushed this code up to let zero-day have a whack at it, and I also > downloaded the latest 8.1.0 cross compilers for all the archs that are > affected and compiled tested them all (and got rid of all the warnings > I introduced as well). > > I marked this all for stable, but in reality it may not need to be ported > as it will probably not be trivial to do so, becaues you'll need to also > fix the architectures that are no longer used (although do we care about > them?). But if someone really cares about correct timings of the function > graph profiler when the options/graph-time is set to zero, then be my > guest. > > Feel free to test this! I'll be pushing this to linux-next and let it > sit there a week or so before pushing it to Linus. > > git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace.git > ftrace/urgent > > Head SHA1: 1ffd62e282a649483afb0bb4d76f7244b3c10075 > > > Steven Rostedt (VMware) (18): > function_graph: Create function_graph_enter() to consolidate architecture code > x86/function_graph: Simplify with function_graph_entry() > ARM: function_graph: Simplify with function_graph_entry() > arm64: function_graph: Simplify with function_graph_entry() > microblaze: function_graph: Simplify with function_graph_entry() > MIPS: function_graph: Simplify with function_graph_entry() > nds32: function_graph: Simplify with function_graph_entry() > parisc: function_graph: Simplify with function_graph_entry() > powerpc/function_graph: Simplify with function_graph_entry() > riscv/function_graph: Simplify with function_graph_entry() > s390/function_graph: Simplify with function_graph_entry() > sh/function_graph: Simplify with function_graph_entry() > sparc/function_graph: Simplify with function_graph_entry() > function_graph: Make ftrace_push_return_trace() static > function_graph: Use new curr_ret_depth to manage depth instead of curr_ret_stack > function_graph: Move return callback before update of curr_ret_stack > function_graph: Reverse the order of pushing the ret_stack and the callback > function_graph: Have profiler use curr_ret_stack and not depth > > ---- > arch/arm/kernel/ftrace.c | 17 +------------ > arch/arm64/kernel/ftrace.c | 15 +---------- > arch/microblaze/kernel/ftrace.c | 15 ++--------- > arch/mips/kernel/ftrace.c | 14 ++--------- > arch/nds32/kernel/ftrace.c | 18 ++----------- > arch/parisc/kernel/ftrace.c | 17 +++---------- > arch/powerpc/kernel/trace/ftrace.c | 15 ++--------- > arch/riscv/kernel/ftrace.c | 14 ++--------- > arch/s390/kernel/ftrace.c | 13 ++-------- > arch/sh/kernel/ftrace.c | 16 ++---------- > arch/sparc/kernel/ftrace.c | 11 +------- > arch/x86/kernel/ftrace.c | 15 +---------- > include/linux/ftrace.h | 4 +-- > include/linux/sched.h | 1 + > kernel/trace/ftrace.c | 7 ++++-- > kernel/trace/trace_functions_graph.c | 49 ++++++++++++++++++++++++++++-------- > 16 files changed, 67 insertions(+), 174 deletions(-) -- Masami Hiramatsu