linux-kernel - [PATCH v2] tracing: Export tracing clock functions

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Message-Id: <1430406624-22609-1-git-send-email-jsnitsel@redhat.com>
Date:	Thu, 30 Apr 2015 08:10:24 -0700
From:	Jerry Snitselaar <jsnitsel@...hat.com>
To:	linux-kernel@...r.kernel.org
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...hat.com>
Subject: [PATCH v2] tracing: Export tracing clock functions

Critical tracepoint hooks should never call anything that takes a lock,
so they are unable to call getrawmonotonic() or ktime_get().

Export the rest of the tracing clock functions so can be used in
tracepoint hooks.

Background: We have a customer that adds their own module and registers
a tracepoint hook to sched_wakeup. They were using ktime_get() for a
time source, but it grabs a seq lock and caused a deadlock to occur.

v2: added background info and fixed typo

Cc: Steven Rostedt <rostedt@...dmis.org>
Cc: Ingo Molnar <mingo@...hat.com>
Signed-off-by: Jerry Snitselaar <jsnitsel@...hat.com>
---
 kernel/trace/trace_clock.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/trace/trace_clock.c b/kernel/trace/trace_clock.c
index 57b67b1..0f06532 100644
--- a/kernel/trace/trace_clock.c
+++ b/kernel/trace/trace_clock.c
@@ -56,6 +56,7 @@ u64 notrace trace_clock(void)
 {
 	return local_clock();
 }
+EXPORT_SYMBOL_GPL(trace_clock);
 
 /*
  * trace_jiffy_clock(): Simply use jiffies as a clock counter.
@@ -68,6 +69,7 @@ u64 notrace trace_clock_jiffies(void)
 {
 	return jiffies_64_to_clock_t(jiffies_64 - INITIAL_JIFFIES);
 }
+EXPORT_SYMBOL_GPL(trace_clock_jiffies);
 
 /*
  * trace_clock_global(): special globally coherent trace clock
@@ -123,6 +125,7 @@ u64 notrace trace_clock_global(void)
 
 	return now;
 }
+EXPORT_SYMBOL_GPL(trace_clock_global);
 
 static atomic64_t trace_counter;
 
-- 
2.4.0.rc3.3.g6eb1401

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