[PATCH] ftrace: only trace preempt off with preempt tracer

[Steven Rostedt]

When PREEMPT_TRACER and IRQSOFF_TRACER are both configured and irqsoff
tracer is running, the preempt_off sections might also be traced.

Thanks to Andrew Morton for pointing out my mistake of spin_lock disabling
interrupts while he was reviewing ftrace.txt. Seems that my example I used
actually hit this bug.

Signed-off-by: Steven Rostedt <srostedt@xxxxxxxxxx>
---
 kernel/trace/trace_irqsoff.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

Index: linus.git/kernel/trace/trace_irqsoff.c
===================================================================
--- linus.git.orig/kernel/trace/trace_irqsoff.c	2008-07-14 23:08:16.000000000 -0400
+++ linus.git/kernel/trace/trace_irqsoff.c	2008-07-15 00:22:59.000000000 -0400
@@ -337,12 +337,14 @@ EXPORT_SYMBOL(trace_hardirqs_off_caller)
 #ifdef CONFIG_PREEMPT_TRACER
 void trace_preempt_on(unsigned long a0, unsigned long a1)
 {
-	stop_critical_timing(a0, a1);
+	if (preempt_trace())
+		stop_critical_timing(a0, a1);
 }

 void trace_preempt_off(unsigned long a0, unsigned long a1)
 {
-	start_critical_timing(a0, a1);
+	if (preempt_trace())
+		start_critical_timing(a0, a1);
 }
 #endif /* CONFIG_PREEMPT_TRACER */


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