ftrace: add ftrace_kill_atomic

It has been suggested that I add a way to disable the function tracer
on an oops. This code adds a ftrace_kill_atomic. It is not meant to be
used in normal situations. It will disable the ftrace tracer, but will
not perform the nice shutdown that requires scheduling.

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

include/linux/ftrace.h

@@ -89,6 +89,7 @@ void ftrace_enable_daemon(void);
 
 /* totally disable ftrace - can not re-enable after this */
 void ftrace_kill(void);
+void ftrace_kill_atomic(void);
 
 static inline void tracer_disable(void)
 {

kernel/trace/ftrace.c

@@ -1601,6 +1601,21 @@ core_initcall(ftrace_dynamic_init);
 # define ftrace_force_shutdown()	do { } while (0)
 #endif /* CONFIG_DYNAMIC_FTRACE */
 
+/**
+ * ftrace_kill_atomic - kill ftrace from critical sections
+ *
+ * This function should be used by panic code. It stops ftrace
+ * but in a not so nice way. If you need to simply kill ftrace
+ * from a non-atomic section, use ftrace_kill.
+ */
+void ftrace_kill_atomic(void)
+{
+	ftrace_disabled = 1;
+	ftrace_enabled = 0;
+	ftraced_suspend = -1;
+	clear_ftrace_function();
+}
+
 /**
  * ftrace_kill - totally shutdown ftrace
  *