From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1042501AbdDUVdq (ORCPT ); Fri, 21 Apr 2017 17:33:46 -0400 Received: from mail.kernel.org ([198.145.29.136]:50878 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1041305AbdDUVdf (ORCPT ); Fri, 21 Apr 2017 17:33:35 -0400 Message-Id: <20170421213328.276813891@goodmis.org> User-Agent: quilt/0.63-1 Date: Fri, 21 Apr 2017 17:30:23 -0400 From: Steven Rostedt To: linux-kernel@vger.kernel.org Cc: Ingo Molnar , Andrew Morton , "Paul E. McKenney" Subject: [for-next][PATCH 03/33] tracing: Have the trace_event benchmark thread call cond_resched_rcu_qs() References: <20170421213020.875637678@goodmis.org> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 Content-Disposition: inline; filename=0003-tracing-Have-the-trace_event-benchmark-thread-call-c.patch Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: "Steven Rostedt (VMware)" The trace_event benchmark thread runs in kernel space in an infinite loop while also calling cond_resched() in case anything else wants to schedule in. Unfortunately, on a PREEMPT kernel, that makes it a nop, in which case, this will never voluntarily schedule. That will cause synchronize_rcu_tasks() to forever block on this thread, while it is running. This is exactly what cond_resched_rcu_qs() is for. Use that instead. Acked-by: "Paul E. McKenney" Signed-off-by: Steven Rostedt (VMware) --- kernel/trace/trace_benchmark.c | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-) diff --git a/kernel/trace/trace_benchmark.c b/kernel/trace/trace_benchmark.c index e49fbe901cfc..16a8cf02eee9 100644 --- a/kernel/trace/trace_benchmark.c +++ b/kernel/trace/trace_benchmark.c @@ -153,10 +153,18 @@ static int benchmark_event_kthread(void *arg) trace_do_benchmark(); /* - * We don't go to sleep, but let others - * run as well. + * We don't go to sleep, but let others run as well. + * This is bascially a "yield()" to let any task that + * wants to run, schedule in, but if the CPU is idle, + * we'll keep burning cycles. + * + * Note the _rcu_qs() version of cond_resched() will + * notify synchronize_rcu_tasks() that this thread has + * passed a quiescent state for rcu_tasks. Otherwise + * this thread will never voluntarily schedule which would + * block synchronize_rcu_tasks() indefinitely. */ - cond_resched(); + cond_resched_rcu_qs(); } return 0; -- 2.10.2