From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934994Ab3IDOjm (ORCPT ); Wed, 4 Sep 2013 10:39:42 -0400 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.122]:14106 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1762811Ab3IDOhH (ORCPT ); Wed, 4 Sep 2013 10:37:07 -0400 X-Authority-Analysis: v=2.0 cv=fJG7LOme c=1 sm=0 a=Sro2XwOs0tJUSHxCKfOySw==:17 a=Drc5e87SC40A:10 a=Ciwy3NGCPMMA:10 a=suUrINWhVCIA:10 a=5SG0PmZfjMsA:10 a=bbbx4UPp9XUA:10 a=meVymXHHAAAA:8 a=KGjhK52YXX0A:10 a=bFSO1-wHURoA:10 a=jREKiASAg2tDcGA6ehgA:9 a=jeBq3FmKZ4MA:10 a=Sro2XwOs0tJUSHxCKfOySw==:117 X-Cloudmark-Score: 0 X-Authenticated-User: X-Originating-IP: 67.255.60.225 Message-Id: <20130904143702.439240564@goodmis.org> User-Agent: quilt/0.60-1 Date: Wed, 04 Sep 2013 10:36:05 -0400 From: Steven Rostedt To: linux-kernel@vger.kernel.org Cc: Ingo Molnar , Frederic Weisbecker , Andrew Morton , Peter Zijlstra , Thomas Gleixner , "Paul E. McKenney" Subject: [for-next][PATCH 13/18] ftrace: Disable RCU unsafe checker when function graph is enabled References: <20130904143552.456506259@goodmis.org> Content-Disposition: inline; filename=0012-ftrace-Disable-RCU-unsafe-checker-when-function-grap.patch Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: "Steven Rostedt (Red Hat)" Having the RCU unsafe checker running when function graph is enabled can cause a live lock. That's because the RCU unsafe checker enables full lockdep debugging on RCU which does a lot of internal calls that may be traced by the function graph tracer. This adds quite a bit of overhead and can possibly live lock the system by causing the timer interrupt to take longer than 1 HZ. Just do not do the RCU unsafe checks when function graph tracer is enabled. Signed-off-by: Steven Rostedt --- kernel/trace/ftrace.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c index 9fcf842..899c8c1 100644 --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -5118,6 +5118,12 @@ int register_ftrace_graph(trace_func_graph_ret_t retfunc, goto out; } + /* + * The Unsafe RCU checker can live lock function graph tracing. + * It's best to just disable it while doing the fgraph tracing. + */ + ftrace_unsafe_rcu_checker_disable(); + ftrace_graph_return = retfunc; ftrace_graph_entry = entryfunc; @@ -5141,6 +5147,7 @@ void unregister_ftrace_graph(void) ftrace_shutdown(&global_ops, FTRACE_STOP_FUNC_RET); unregister_pm_notifier(&ftrace_suspend_notifier); unregister_trace_sched_switch(ftrace_graph_probe_sched_switch, NULL); + ftrace_unsafe_rcu_checker_enable(); out: mutex_unlock(&ftrace_lock); -- 1.7.10.4