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=-15.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,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 0C9C6C433FE for ; Thu, 23 Sep 2021 13:34:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DF7EA61164 for ; Thu, 23 Sep 2021 13:34:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241415AbhIWNfe convert rfc822-to-8bit (ORCPT ); Thu, 23 Sep 2021 09:35:34 -0400 Received: from mail.kernel.org ([198.145.29.99]:46924 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241205AbhIWNfc (ORCPT ); Thu, 23 Sep 2021 09:35:32 -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 C2BB56115A; Thu, 23 Sep 2021 13:34:00 +0000 (UTC) Date: Thu, 23 Sep 2021 09:33:59 -0400 From: Steven Rostedt To: =?UTF-8?B?546L6LSH?= Cc: Ingo Molnar , open list Subject: Re: [RFC PATCH] trace: prevent preemption in perf_ftrace_function_call() Message-ID: <20210923093359.30da8ba6@gandalf.local.home> In-Reply-To: <2470f39b-aed1-4e19-9982-206007eb0c6a@linux.alibaba.com> References: <2470f39b-aed1-4e19-9982-206007eb0c6a@linux.alibaba.com> X-Mailer: Claws Mail 3.17.8 (GTK+ 2.24.33; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 23 Sep 2021 11:42:56 +0800 王贇 wrote: > With CONFIG_DEBUG_PREEMPT we observed reports like: > > BUG: using smp_processor_id() in preemptible > caller is perf_ftrace_function_call+0x6f/0x2e0 > CPU: 1 PID: 680 Comm: a.out Not tainted > Call Trace: > > dump_stack_lvl+0x8d/0xcf > check_preemption_disabled+0x104/0x110 > ? optimize_nops.isra.7+0x230/0x230 > ? text_poke_bp_batch+0x9f/0x310 > perf_ftrace_function_call+0x6f/0x2e0 > ... > __text_poke+0x5/0x620 > text_poke_bp_batch+0x9f/0x310 > > This tell us the CPU could be changed after task is preempted, and > the checking on CPU before preemption is helpless. > > This patch just turn off preemption in perf_ftrace_function_call() > to prevent CPU changing. > > Signed-off-by: Michael Wang > --- > kernel/trace/trace_event_perf.c | 14 +++++++++----- > 1 file changed, 9 insertions(+), 5 deletions(-) > > diff --git a/kernel/trace/trace_event_perf.c b/kernel/trace/trace_event_perf.c > index 6aed10e..5486b18 100644 > --- a/kernel/trace/trace_event_perf.c > +++ b/kernel/trace/trace_event_perf.c > @@ -438,15 +438,17 @@ void perf_trace_buf_update(void *record, u16 type) > int rctx; > int bit; > > + preempt_disable_notrace(); > + > if (!rcu_is_watching()) > - return; > + goto out; You don't need preemption disabled for the above check. It's better to disable it here and leave the above return untouched. -- Steve > > if ((unsigned long)ops->private != smp_processor_id()) > - return; > + goto out; > > bit = ftrace_test_recursion_trylock(ip, parent_ip); > if (bit < 0) > - return; > + goto out; > > event = container_of(ops, struct perf_event, ftrace_ops); > > @@ -468,16 +470,18 @@ void perf_trace_buf_update(void *record, u16 type) > > entry = perf_trace_buf_alloc(ENTRY_SIZE, NULL, &rctx); > if (!entry) > - goto out; > + goto out_unlock; > > entry->ip = ip; > entry->parent_ip = parent_ip; > perf_trace_buf_submit(entry, ENTRY_SIZE, rctx, TRACE_FN, > 1, ®s, &head, NULL); > > -out: > +out_unlock: > ftrace_test_recursion_unlock(bit); > #undef ENTRY_SIZE > +out: > + preempt_enable_notrace(); > } > > static int perf_ftrace_function_register(struct perf_event *event)