From c8943ed663e1f105a4e083ed567f90d8783684fc Mon Sep 17 00:00:00 2001
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Wed, 25 May 2016 14:03:50 +0200
Subject: [PATCH 345/398] trace: correct off by one while recording the
 trace-event

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.

Cc: stable-rt@vger.kernel.org
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
[ Changed this to upstream version. See commit e947841c0dce ]
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 kernel/trace/trace_events.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index 2105d5f1c396..e43e45a2aa7e 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -246,6 +246,14 @@ void *trace_event_buffer_reserve(struct trace_event_buffer *fbuffer,
 
 	local_save_flags(fbuffer->flags);
 	fbuffer->pc = preempt_count();
+	/*
+	 * If CONFIG_PREEMPT is enabled, then the tracepoint itself disables
+	 * preemption (adding one to the preempt_count). Since we are
+	 * interested in the preempt_count at the time the tracepoint was
+	 * hit, we need to subtract one to offset the increment.
+	 */
+	if (IS_ENABLED(CONFIG_PREEMPT))
+		fbuffer->pc--;
 	fbuffer->trace_file = trace_file;
 
 	fbuffer->event =
-- 
2.14.4

