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=-15.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_2 autolearn=unavailable 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 EBE98C4361B for ; Mon, 14 Dec 2020 15:25:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8FD1722B3B for ; Mon, 14 Dec 2020 15:25:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2392388AbgLNPZk (ORCPT ); Mon, 14 Dec 2020 10:25:40 -0500 Received: from mail.kernel.org ([198.145.29.99]:54792 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2405383AbgLNPZF (ORCPT ); Mon, 14 Dec 2020 10:25:05 -0500 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 CD59222A99; Mon, 14 Dec 2020 15:24:23 +0000 (UTC) Date: Mon, 14 Dec 2020 10:24:22 -0500 From: Steven Rostedt To: Ming Lei Cc: Jens Axboe , linux-block@vger.kernel.org, Christoph Hellwig , Ingo Molnar , linux-kernel@vger.kernel.org, linux-rt-users Subject: Re: [PATCH] blktrace: fix 'BUG: sleeping function called from invalid context' in case of PREEMPT_RT Message-ID: <20201214102422.2d84035d@gandalf.local.home> In-Reply-To: <20201214022217.1754273-1-ming.lei@redhat.com> References: <20201214022217.1754273-1-ming.lei@redhat.com> 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 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 14 Dec 2020 10:22:17 +0800 Ming Lei wrote: > trace_note_tsk() is called by __blk_add_trace(), which is covered by RCU read lock. > So in case of PREEMPT_RT, warning of 'BUG: sleeping function called from invalid context' > will be triggered because spin lock is converted to rtmutex. The RCU read_lock() can not be the cause of this issue, because under PREEMPT_RT, rcu_read_lock() can be preempted. What was the full back trace of this problem? > > Fix the issue by converting running_trace_lock into raw_spin_lock(). > > Cc: Christoph Hellwig > Cc: Steven Rostedt > Cc: Ingo Molnar > Cc: linux-kernel@vger.kernel.org > Signed-off-by: Ming Lei > --- > kernel/trace/blktrace.c | 14 +++++++------- > 1 file changed, 7 insertions(+), 7 deletions(-) > > diff --git a/kernel/trace/blktrace.c b/kernel/trace/blktrace.c > index 2c5b3c5317c2..53dc876d669d 100644 > --- a/kernel/trace/blktrace.c > +++ b/kernel/trace/blktrace.c > @@ -34,7 +34,7 @@ static struct trace_array *blk_tr; > static bool blk_tracer_enabled __read_mostly; > > static LIST_HEAD(running_trace_list); > -static __cacheline_aligned_in_smp DEFINE_SPINLOCK(running_trace_lock); > +static __cacheline_aligned_in_smp DEFINE_RAW_SPINLOCK(running_trace_lock); > > /* Select an alternative, minimalistic output than the original one */ > #define TRACE_BLK_OPT_CLASSIC 0x1 > @@ -121,12 +121,12 @@ static void trace_note_tsk(struct task_struct *tsk) > struct blk_trace *bt; > > tsk->btrace_seq = blktrace_seq; > - spin_lock_irqsave(&running_trace_lock, flags); > + raw_spin_lock_irqsave(&running_trace_lock, flags); > list_for_each_entry(bt, &running_trace_list, running_list) { > trace_note(bt, tsk->pid, BLK_TN_PROCESS, tsk->comm, > sizeof(tsk->comm), 0); > } How big is this running_trace_list? May not be something we want raw locks around. Please understand that converting locks to raw should be the last resort. One should always look at the reason for a spin lock in a preempt disabled area and see if there's other means of solving it before simply switch a lock to raw, as each raw spinlock makes PREEMPT_RT less real time. -- Steve > - spin_unlock_irqrestore(&running_trace_lock, flags); > + raw_spin_unlock_irqrestore(&running_trace_lock, flags); > } > > static void trace_note_time(struct blk_trace *bt) > @@ -669,9 +669,9 @@ static int __blk_trace_startstop(struct request_queue *q, int start) > blktrace_seq++; > smp_mb(); > bt->trace_state = Blktrace_running; > - spin_lock_irq(&running_trace_lock); > + raw_spin_lock_irq(&running_trace_lock); > list_add(&bt->running_list, &running_trace_list); > - spin_unlock_irq(&running_trace_lock); > + raw_spin_unlock_irq(&running_trace_lock); > > trace_note_time(bt); > ret = 0; > @@ -679,9 +679,9 @@ static int __blk_trace_startstop(struct request_queue *q, int start) > } else { > if (bt->trace_state == Blktrace_running) { > bt->trace_state = Blktrace_stopped; > - spin_lock_irq(&running_trace_lock); > + raw_spin_lock_irq(&running_trace_lock); > list_del_init(&bt->running_list); > - spin_unlock_irq(&running_trace_lock); > + raw_spin_unlock_irq(&running_trace_lock); > relay_flush(bt->rchan); > ret = 0; > }