[PATCH 3/5] tracing/events: add rcu locking around trace event prints

[Steven Rostedt <rostedt@goodmis.org>]

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From: Steven Rostedt <srostedt@redhat.com>

Some trace events need to have a way to print out data that his
allocated, but will be freed later. Using a function that can allocate
memory, and free it with call_rcu, can be useful.

This patch adds rcu locking around the print part of the TRACE_EVENT
macro to facilitate this.

Reported-by: Theodore Tso <tytso@mit.edu>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 include/trace/ftrace.h |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)

diff --git a/include/trace/ftrace.h b/include/trace/ftrace.h
index 60c5323..6fb06bd 100644
--- a/include/trace/ftrace.h
+++ b/include/trace/ftrace.h
@@ -62,7 +62,9 @@
  *
  *	field = (typeof(field))entry;
  *
+ *	rcu_read_lock();
  *	ret = trace_seq_printf(s, <TP_printk> "\n");
+ *	rcu_read_unlock();
  *	if (!ret)
  *		return TRACE_TYPE_PARTIAL_LINE;
  *
@@ -99,7 +101,9 @@ ftrace_raw_output_##call(struct trace_iterator *iter, int flags)	\
 									\
 	field = (typeof(field))entry;					\
 									\
+	rcu_read_lock();						\
 	ret = trace_seq_printf(s, #call ": " print);			\
+	rcu_read_unlock();						\
 	if (!ret)							\
 		return TRACE_TYPE_PARTIAL_LINE;				\
 									\
-- 
1.6.2.1

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