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=-0.9 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, 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 C6A5DC04A6B for ; Wed, 8 May 2019 16:53:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A10042173B for ; Wed, 8 May 2019 16:53:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728828AbfEHQxk (ORCPT ); Wed, 8 May 2019 12:53:40 -0400 Received: from mail.kernel.org ([198.145.29.99]:55048 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728679AbfEHQxj (ORCPT ); Wed, 8 May 2019 12:53:39 -0400 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 C3E6A20850; Wed, 8 May 2019 16:53:38 +0000 (UTC) Date: Wed, 8 May 2019 12:53:37 -0400 From: Steven Rostedt To: "chengjian (D)" Cc: , , , , Subject: Re: [PATCH] ftrace: enable trampoline when rec count decrement to one Message-ID: <20190508125337.37777a2f@gandalf.local.home> In-Reply-To: References: <1556969979-111047-1-git-send-email-cj.chengjian@huawei.com> <20190505153447.594d4eab@oasis.local.home> 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, 8 May 2019 23:02:33 +0800 "chengjian (D)" wrote: > function tracer uses ftrace_caller() and livepatch uses > ftrace_regs_caller(). > > I can modify my testcase to trigger this race condition. > > > #enable livepatch > insmod klp_unshare_files.ko > cat /sys/kernel/debug/tracing/enabled_functions > unshare_files (1) R I tramp: 0xffffffffc0008000 (klp_ftrace_handler+0x0/0xa0) ->ftrace_ops_assist_func+0x0/0xf0 > [NOW, the rec caller is ftracer_regs_caller TRAMPOLINE] > > #function tracer > echo unshare_files > /sys/kernel/debug/tracing/set_ftrace_filter > echo function > /sys/kernel/debug/tracing/current_tracer > cat /sys/kernel/debug/tracing/enabled_functions > unshare_files (2) R I ->ftrace_ops_list_func+0x0/0x170 > [NOW, the rec caller is ftracer_regs_caller] > > > # disable livepatch > echo 0 > /sys/kernel/livepatch/klp_unshare_files/enabled > rmmod klp_unshare_files > > > cat /sys/kernel/debug/tracing/enabled_functions > unshare_files (1) tramp: 0xffffffffc0005000 (function_trace_call+0x0/0x120) ->function_trace_call+0x0/0x120 > [NOW, the rec caller is ftrace_caller TRAMPOLINE] > > So, the caller switch from regs caller back to non regs caller > when disable the livepatch. Could this testcase cause the race > condition ? BUT, Nothing happened here. > > What will happen when the race triggers ? What can I do. > I still can't think of it. But since the merge window already opened, I'd like to have this patch sit in linux-next for a bit. That is, I would wait to pull it in for the next merge window, and not this one. -- Steve