[PATCH RT 2/4] trace: correct off by one while recording the trace-event

[Steven Rostedt]

3.2.81-rt117-rc1 stable review patch.
If anyone has any objections, please let me know.

------------------

From: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>

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@xxxxxxxxxxxxxxx
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
[ Changed this to upstream version. See commit e947841c0dce ]
Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
---
 include/trace/ftrace.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h
index 763bf05ccb27..73aab555b42d 100644
--- a/include/trace/ftrace.h
+++ b/include/trace/ftrace.h
@@ -530,6 +530,9 @@ ftrace_raw_event_##call(void *__data, proto)				\
 									\
 	local_save_flags(irq_flags);					\
 	pc = preempt_count();						\
+	/* Account for tracepoint preempt disable */			\
+	if (IS_ENABLED(CONFIG_PREEMPT))					\
+		pc--;							\
 									\
 	__data_size = ftrace_get_offsets_##call(&__data_offsets, args); \
 									\
-- 
2.8.1