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authorSteven Rostedt (Red Hat) <rostedt@goodmis.org>2016-06-17 17:40:58 -0400
committerSteven Rostedt <rostedt@goodmis.org>2016-06-20 09:54:21 -0400
commite947841c0dce9db675a957182214ef8091ac3d61 (patch)
tree8388467c005b99695103a85f03a9b21a6194b5b0 /kernel/trace
parentaad108aa9d1aca5be178ef40325dcc99b448e866 (diff)
downloadop-kernel-dev-e947841c0dce9db675a957182214ef8091ac3d61.zip
op-kernel-dev-e947841c0dce9db675a957182214ef8091ac3d61.tar.gz
tracing: Show the preempt count of when the event was called
Because tracepoint callbacks are done with preemption enabled, the trace events are always called with preempt disable due to the rcu_read_lock_sched_notrace() in __DO_TRACE(). This causes the preempt count shown in the recorded trace event to be inaccurate. It is always one more that what the preempt_count was when the tracepoint was called. If CONFIG_PREEMPT is enabled, subtract 1 from the preempt_count before recording it in the trace buffer. Link: http://lkml.kernel.org/r/20160525132537.GA10808@linutronix.de Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Diffstat (limited to 'kernel/trace')
-rw-r--r--kernel/trace/trace_events.c8
1 files changed, 8 insertions, 0 deletions
diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c
index fd449eb..03c0a48 100644
--- a/kernel/trace/trace_events.c
+++ b/kernel/trace/trace_events.c
@@ -261,6 +261,14 @@ 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 =
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