From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754949AbcEYNZo (ORCPT ); Wed, 25 May 2016 09:25:44 -0400 Received: from www.linutronix.de ([62.245.132.108]:40313 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754474AbcEYNZn (ORCPT ); Wed, 25 May 2016 09:25:43 -0400 Date: Wed, 25 May 2016 15:25:37 +0200 From: Sebastian Andrzej Siewior To: Steven Rostedt Cc: Ingo Molnar , linux-kernel@vger.kernel.org, tglx@linutronix.de Subject: [PATCH RFC] trace: correct off by one preempt counter while recording the trace-event Message-ID: <20160525132537.GA10808@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Trace events like raw_syscalls show always a preempt code of one. The reason is that on PREEMPT kernels rcu_read_lock_sched_notrace() increases the preemption counter and the function recording the counter is caller within the RCU section. Signed-off-by: Sebastian Andrzej Siewior --- I am not sure if this is the only spot that needs correction of the preemption counter. If it is it could be corrected directly in trace_event_buffer_reserve(). include/linux/tracepoint.h | 13 +++++++++++++ kernel/trace/trace_events.c | 2 +- 2 files changed, 14 insertions(+), 1 deletion(-) diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h index be586c632a0c..12cb3bb40c1c 100644 --- a/include/linux/tracepoint.h +++ b/include/linux/tracepoint.h @@ -33,6 +33,19 @@ struct trace_enum_map { #define TRACEPOINT_DEFAULT_PRIO 10 +/* + * The preempt count recorded in trace_event_raw_event_# are off by one due to + * rcu_read_lock_sched_notrace() in __DO_TRACE. This is corrected here. + */ +static inline int event_preempt_count(void) +{ +#ifdef CONFIG_PREEMPT + return preempt_count() - 1; +#else + return 0; +#endif +} + extern int tracepoint_probe_register(struct tracepoint *tp, void *probe, void *data); extern int diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c index 52c4fffaddcd..90b40cf6ec98 100644 --- a/kernel/trace/trace_events.c +++ b/kernel/trace/trace_events.c @@ -245,7 +245,7 @@ void *trace_event_buffer_reserve(struct trace_event_buffer *fbuffer, return NULL; local_save_flags(fbuffer->flags); - fbuffer->pc = preempt_count(); + fbuffer->pc = event_preempt_count(); fbuffer->trace_file = trace_file; fbuffer->event = -- 2.8.1