ftrace: make some tracers reentrant

Now that the ring buffer is reentrant, some of the ftrace tracers
(sched_swich, debugging traces) can also be reentrant.

Note: Never make the function tracer reentrant, that can cause
  recursion problems all over the kernel. The function tracer
  must disable reentrancy.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

kernel/trace/trace.c

@@ -839,7 +839,6 @@ ftrace_special(unsigned long arg1, unsigned long arg2, unsigned long arg3)
 {
 	struct trace_array *tr = &global_trace;
 	struct trace_array_cpu *data;
-	long disabled;
 	int cpu;
 	int pc;
 
@@ -850,12 +849,10 @@ ftrace_special(unsigned long arg1, unsigned long arg2, unsigned long arg3)
 	preempt_disable_notrace();
 	cpu = raw_smp_processor_id();
 	data = tr->data[cpu];
-	disabled = atomic_inc_return(&data->disabled);
 
-	if (likely(disabled == 1))
+	if (likely(!atomic_read(&data->disabled)))
 		ftrace_trace_special(tr, data, arg1, arg2, arg3, pc);
 
-	atomic_dec(&data->disabled);
 	preempt_enable_notrace();
 }
 
@@ -2961,7 +2958,6 @@ int trace_vprintk(unsigned long ip, const char *fmt, va_list args)
 	struct trace_array_cpu *data;
 	struct print_entry *entry;
 	unsigned long flags, irq_flags;
-	long disabled;
 	int cpu, len = 0, size, pc;
 
 	if (!tr->ctrl || tracing_disabled)
@@ -2971,9 +2967,8 @@ int trace_vprintk(unsigned long ip, const char *fmt, va_list args)
 	preempt_disable_notrace();
 	cpu = raw_smp_processor_id();
 	data = tr->data[cpu];
-	disabled = atomic_inc_return(&data->disabled);
 
-	if (unlikely(disabled != 1))
+	if (unlikely(atomic_read(&data->disabled)))
 		goto out;
 
 	spin_lock_irqsave(&trace_buf_lock, flags);
@@ -2999,7 +2994,6 @@ int trace_vprintk(unsigned long ip, const char *fmt, va_list args)
 	spin_unlock_irqrestore(&trace_buf_lock, flags);
 
  out:
-	atomic_dec(&data->disabled);
 	preempt_enable_notrace();
 
 	return len;

kernel/trace/trace_sched_switch.c

@@ -24,7 +24,6 @@ probe_sched_switch(struct rq *__rq, struct task_struct *prev,
 {
 	struct trace_array_cpu *data;
 	unsigned long flags;
-	long disabled;
 	int cpu;
 	int pc;
 
@@ -41,12 +40,10 @@ probe_sched_switch(struct rq *__rq, struct task_struct *prev,
 	local_irq_save(flags);
 	cpu = raw_smp_processor_id();
 	data = ctx_trace->data[cpu];
-	disabled = atomic_inc_return(&data->disabled);
 
-	if (likely(disabled == 1))
+	if (likely(!atomic_read(&data->disabled)))
 		tracing_sched_switch_trace(ctx_trace, data, prev, next, flags, pc);
 
-	atomic_dec(&data->disabled);
 	local_irq_restore(flags);
 }
 
@@ -55,7 +52,6 @@ probe_sched_wakeup(struct rq *__rq, struct task_struct *wakee)
 {
 	struct trace_array_cpu *data;
 	unsigned long flags;
-	long disabled;
 	int cpu, pc;
 
 	if (!likely(tracer_enabled))
@@ -67,13 +63,11 @@ probe_sched_wakeup(struct rq *__rq, struct task_struct *wakee)
 	local_irq_save(flags);
 	cpu = raw_smp_processor_id();
 	data = ctx_trace->data[cpu];
-	disabled = atomic_inc_return(&data->disabled);
 
-	if (likely(disabled == 1))
+	if (likely(!atomic_read(&data->disabled)))
 		tracing_sched_wakeup_trace(ctx_trace, data, wakee, current,
 					   flags, pc);
 
-	atomic_dec(&data->disabled);
 	local_irq_restore(flags);
 }