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=-1.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_PASS,T_DKIMWL_WL_HIGH,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 DD443C28CF6 for ; Fri, 3 Aug 2018 07:32:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 902B32172B for ; Fri, 3 Aug 2018 07:32:15 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="eCrhZ0aE" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 902B32172B 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 S1728947AbeHCJ1M (ORCPT ); Fri, 3 Aug 2018 05:27:12 -0400 Received: from mail.kernel.org ([198.145.29.99]:57134 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727652AbeHCJ1M (ORCPT ); Fri, 3 Aug 2018 05:27:12 -0400 Received: from devbox (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 CC92B2170A; Fri, 3 Aug 2018 07:32:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1533281532; bh=JyUTnRKLYs46FFbTE13GHcqilFhvX0hkHdMzcvaN5vc=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=eCrhZ0aEPK4w04kpE9GS8y634MveY46V2AOkKaGcDVWzmnK0yytosS6cWF7PRvujj xpzf261CUXRQYy/CF7yiwZuFtBN8fCW30iNXocAYCn2dUUrVk5YSwTjS5Z3h5S32L+ mfn/EPbzDTtIl2VEuP7i1zzr1Tz/uCOg7/7X4idI= Date: Fri, 3 Aug 2018 16:32:09 +0900 From: Masami Hiramatsu To: "Joel Fernandes (Google)" Cc: linux-kernel@vger.kernel.org, kernel-team@android.com, Ingo Molnar , Steven Rostedt , mathieu.desnoyers@efficios.com, mhiramat@kernel.org, paulmck@linux.vnet.ibm.com, peterz@infradead.org Subject: Re: [PATCH] trace: Use rcu_dereference_raw for hooks from trace-event subsystem Message-Id: <20180803163209.20ebd9dc3f25fd9994764370@kernel.org> In-Reply-To: <20180803023407.225852-1-joel@joelfernandes.org> References: <20180803023407.225852-1-joel@joelfernandes.org> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.31; x86_64-redhat-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 Thu, 2 Aug 2018 19:34:07 -0700 "Joel Fernandes (Google)" wrote: > Since we switched to using SRCU for tracepoints used in the idle path, > we can no longer use rcu_dereference_sched for dereferencing points in > trace-event hooks. > > Since tracepoints can now use either SRCU or sched-RCU, just use > rcu_dereference_raw for traceevents just like we're doing when > dereferencing the tracepoint table. OK, I've tested that this fixes the bug. /mnt/ftrace # ./ftracetest test.d/event/toplevel-enable.tc === Ftrace unit tests === [1] event tracing - enable/disable with top level files [PASS] # of passed: 1 # of failed: 0 # of unresolved: 0 # of untested: 0 # of unsupported: 0 # of xfailed: 0 # of undefined(test bug): 0 Tested-by: Masami Hiramatsu Thank you! > > This prevents an RCU warning reported by Masami: > > [ 282.060593] WARNING: can't dereference registers at 00000000f3c7f62b > [ 282.063200] ============================= > [ 282.064082] WARNING: suspicious RCU usage > [ 282.064963] 4.18.0-rc6+ #15 Tainted: G W > [ 282.066048] ----------------------------- > [ 282.066923] /home/mhiramat/ksrc/linux/kernel/trace/trace_events.c:242 > suspicious rcu_dereference_check() usage! > [ 282.068974] > [ 282.068974] other info that might help us debug this: > [ 282.068974] > [ 282.070770] > [ 282.070770] RCU used illegally from idle CPU! > [ 282.070770] rcu_scheduler_active = 2, debug_locks = 1 > [ 282.072938] RCU used illegally from extended quiescent state! > [ 282.074183] no locks held by swapper/0/0. > [ 282.075071] > [ 282.075071] stack backtrace: > [ 282.076121] CPU: 0 PID: 0 Comm: swapper/0 Tainted: G W > [ 282.077782] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996) > [ 282.079604] Call Trace: > [ 282.080212] > [ 282.080755] dump_stack+0x85/0xcb > [ 282.081523] trace_event_ignore_this_pid+0x66/0x70 > [ 282.082541] trace_event_raw_event_preemptirq_template+0xa2/0xb0 > [ 282.083774] ? interrupt_entry+0xc4/0xe0 > [ 282.084665] ? trace_hardirqs_off_thunk+0x1a/0x1c > [ 282.085669] trace_hardirqs_off_caller+0x90/0xd0 > [ 282.086597] trace_hardirqs_off_thunk+0x1a/0x1c > [ 282.087433] ? call_function_interrupt+0xa/0x20 > [ 282.088201] interrupt_entry+0xc4/0xe0 > [ 282.088848] ? call_function_interrupt+0xa/0x20 > [ 282.089579] > [ 282.090029] ? native_safe_halt+0x2/0x10 > [ 282.090695] ? default_idle+0x1f/0x160 > [ 282.091330] ? default_idle_call+0x24/0x40 > [ 282.091997] ? do_idle+0x210/0x250 > [ 282.092658] ? cpu_startup_entry+0x6f/0x80 > [ 282.093338] ? start_kernel+0x49d/0x4bd > [ 282.093987] ? secondary_startup_64+0xa5/0xb0 > > Reported-by: Masami Hiramatsu > Fixes: e6753f23d961 ("tracepoint: Make rcuidle tracepoint callers use SRCU") > Signed-off-by: Joel Fernandes (Google) > --- > kernel/trace/trace_events.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c > index 14ff4ff3caab..7b508ce8ac44 100644 > --- a/kernel/trace/trace_events.c > +++ b/kernel/trace/trace_events.c > @@ -239,7 +239,7 @@ bool trace_event_ignore_this_pid(struct trace_event_file *trace_file) > struct trace_array_cpu *data; > struct trace_pid_list *pid_list; > > - pid_list = rcu_dereference_sched(tr->filtered_pids); > + pid_list = rcu_dereference_raw(tr->filtered_pids); > if (!pid_list) > return false; > > @@ -512,7 +512,7 @@ event_filter_pid_sched_process_exit(void *data, struct task_struct *task) > struct trace_pid_list *pid_list; > struct trace_array *tr = data; > > - pid_list = rcu_dereference_sched(tr->filtered_pids); > + pid_list = rcu_dereference_raw(tr->filtered_pids); > trace_filter_add_remove_task(pid_list, NULL, task); > } > > -- > 2.18.0.597.ga71716f1ad-goog > -- Masami Hiramatsu