ftrace: fix updates to max trace

This patch fixes some bugs to the updating of the max trace that
was caused by implementing the new buffering.

Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 15 insertions, 12 deletions

diff --git a/kernel/trace/trace_irqsoff.c b/kernel/trace/trace_irqsoff.c
index bd3f88198308..74165f611f36 100644
--- a/kernel/trace/trace_irqsoff.c
+++ b/kernel/trace/trace_irqsoff.c
@@ -23,6 +23,8 @@ static int				tracer_enabled __read_mostly;
 
 static DEFINE_PER_CPU(int, tracing_cpu);
 
+static DEFINE_SPINLOCK(max_trace_lock);
+
 enum {
         TRACER_IRQS_OFF         = (1 << 1),
         TRACER_PREEMPT_OFF      = (1 << 2),
@@ -126,7 +128,7 @@ check_critical_timing(struct trace_array *tr,
                       int cpu)
 {
         unsigned long latency, t0, t1;
-        cycle_t T0, T1, T2, delta;
+        cycle_t T0, T1, delta;
         unsigned long flags;
 
         /*
@@ -142,20 +144,18 @@ check_critical_timing(struct trace_array *tr,
         if (!report_latency(delta))
                 goto out;
 
-        ftrace(tr, data, CALLER_ADDR0, parent_ip, flags);
-        /*
-         * Update the timestamp, because the trace entry above
-         * might change it (it can only get larger so the latency
-         * is fair to be reported):
-         */
-        T2 = now(cpu);
+        spin_lock(&max_trace_lock);
 
-        delta = T2-T0;
+        /* check if we are still the max latency */
+        if (!report_latency(delta))
+                goto out_unlock;
+
+        ftrace(tr, data, CALLER_ADDR0, parent_ip, flags);
 
         latency = nsecs_to_usecs(delta);
 
         if (data->critical_sequence != max_sequence)
-                goto out;
+                goto out_unlock;
 
         tracing_max_latency = delta;
         t0 = nsecs_to_usecs(T0);
@@ -189,6 +189,9 @@ check_critical_timing(struct trace_array *tr,
 
         max_sequence++;
 
+out_unlock:
+        spin_unlock(&max_trace_lock);
+
 out:
         data->critical_sequence = max_sequence;
         data->preempt_timestamp = now(cpu);
@@ -366,14 +369,14 @@ void notrace trace_preempt_off(unsigned long a0, unsigned long a1)
 
 static void start_irqsoff_tracer(struct trace_array *tr)
 {
-        tracer_enabled = 1;
         register_ftrace_function(&trace_ops);
+        tracer_enabled = 1;
 }
 
 static void stop_irqsoff_tracer(struct trace_array *tr)
 {
-        unregister_ftrace_function(&trace_ops);
         tracer_enabled = 0;
+        unregister_ftrace_function(&trace_ops);
 }
 
 static void __irqsoff_tracer_init(struct trace_array *tr)