This includes three fixes. Two fix features added in 3.9 and one

fixes a long time minor bug.
 
 The first patch fixes a race that can happen if the user switches
 from the irqsoff tracer to another tracer. If a irqs off latency is
 detected, it will try to use the snapshot buffer, but the new tracer
 wont have it allocated. There's a nasty warning that gets printed and
 the trace is ignored. Nothing crashes, just a nasty WARN_ON is shown.
 
 The second patch fixes an issue where if the sysctl is used to disable
 and enable function tracing, it can put the function tracing into an
 unstable state.
 
 The third patch fixes an issue with perf using the function tracer.
 An update was done, where the stub function could be called during
 the perf function tracing, and that stub function wont have the
 "control" flag set and cause a nasty warning when running perf.
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Merge tag 'trace-fixes-3.9-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace

Pull tracing fixes from Steven Rostedt:
 "This includes three fixes.  Two fix features added in 3.9 and one
  fixes a long time minor bug.

  The first patch fixes a race that can happen if the user switches from
  the irqsoff tracer to another tracer.  If a irqs off latency is
  detected, it will try to use the snapshot buffer, but the new tracer
  wont have it allocated.  There's a nasty warning that gets printed and
  the trace is ignored.  Nothing crashes, just a nasty WARN_ON is shown.

  The second patch fixes an issue where if the sysctl is used to disable
  and enable function tracing, it can put the function tracing into an
  unstable state.

  The third patch fixes an issue with perf using the function tracer.
  An update was done, where the stub function could be called during the
  perf function tracing, and that stub function wont have the "control"
  flag set and cause a nasty warning when running perf."

* tag 'trace-fixes-3.9-rc6' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt/linux-trace:
  ftrace: Do not call stub functions in control loop
  ftrace: Consistently restore trace function on sysctl enabling
  tracing: Fix race with update_max_tr_single and changing tracers

include/linux/ftrace.h

@@ -89,6 +89,7 @@ typedef void (*ftrace_func_t)(unsigned long ip, unsigned long parent_ip,
  *            that the call back has its own recursion protection. If it does
  *            not set this, then the ftrace infrastructure will add recursion
  *            protection for the caller.
+ * STUB   - The ftrace_ops is just a place holder.
  */
 enum {
 	FTRACE_OPS_FL_ENABLED			= 1 << 0,
@@ -98,6 +99,7 @@ enum {
 	FTRACE_OPS_FL_SAVE_REGS			= 1 << 4,
 	FTRACE_OPS_FL_SAVE_REGS_IF_SUPPORTED	= 1 << 5,
 	FTRACE_OPS_FL_RECURSION_SAFE		= 1 << 6,
+	FTRACE_OPS_FL_STUB			= 1 << 7,
 };
 
 struct ftrace_ops {

kernel/trace/ftrace.c

@@ -66,7 +66,7 @@
 
 static struct ftrace_ops ftrace_list_end __read_mostly = {
 	.func		= ftrace_stub,
-	.flags		= FTRACE_OPS_FL_RECURSION_SAFE,
+	.flags		= FTRACE_OPS_FL_RECURSION_SAFE | FTRACE_OPS_FL_STUB,
 };
 
 /* ftrace_enabled is a method to turn ftrace on or off */
@@ -4131,7 +4131,8 @@ ftrace_ops_control_func(unsigned long ip, unsigned long parent_ip,
 	preempt_disable_notrace();
 	trace_recursion_set(TRACE_CONTROL_BIT);
 	do_for_each_ftrace_op(op, ftrace_control_list) {
-		if (!ftrace_function_local_disabled(op) &&
+		if (!(op->flags & FTRACE_OPS_FL_STUB) &&
+		    !ftrace_function_local_disabled(op) &&
 		    ftrace_ops_test(op, ip))
 			op->func(ip, parent_ip, op, regs);
 	} while_for_each_ftrace_op(op);
@@ -4555,12 +4556,8 @@ ftrace_enable_sysctl(struct ctl_table *table, int write,
 		ftrace_startup_sysctl();
 
 		/* we are starting ftrace again */
-		if (ftrace_ops_list != &ftrace_list_end) {
-			if (ftrace_ops_list->next == &ftrace_list_end)
-				ftrace_trace_function = ftrace_ops_list->func;
-			else
-				ftrace_trace_function = ftrace_ops_list_func;
-		}
+		if (ftrace_ops_list != &ftrace_list_end)
+			update_ftrace_function();
 
 	} else {
 		/* stopping ftrace calls (just send to ftrace_stub) */

kernel/trace/trace.c

@@ -744,8 +744,11 @@ update_max_tr_single(struct trace_array *tr, struct task_struct *tsk, int cpu)
 		return;
 
 	WARN_ON_ONCE(!irqs_disabled());
-	if (WARN_ON_ONCE(!current_trace->allocated_snapshot))
+	if (!current_trace->allocated_snapshot) {
+		/* Only the nop tracer should hit this when disabling */
+		WARN_ON_ONCE(current_trace != &nop_trace);
 		return;
+	}
 
 	arch_spin_lock(&ftrace_max_lock);