[PATCH RT 09/11] trace: correct off by one while recording the trace-event

From: Steven Rostedt
Date: Tue Jul 12 2016 - 12:52:57 EST


3.12.61-rt82-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 645d749d3c9c..1c74dcd4c76e 100644
--- a/include/trace/ftrace.h
+++ b/include/trace/ftrace.h
@@ -536,6 +536,9 @@ 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