ftrace: only trace preempt off with preempt tracer

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@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/kernel/trace/trace_irqsoff.c b/kernel/trace/trace_irqsoff.c
index 421d6fe3650eded0e30ed86105de823c344beb3d..b1e4a89b08eb5bf7118e33be5cb27939dd600691 100644 (file)
--- a/kernel/trace/trace_irqsoff.c
+++ b/kernel/trace/trace_irqsoff.c
@@ -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 */