ftrace: add ftrace_off_permanent

Impact: add new API to disable all of ftrace on anomalies

It case of a serious anomaly being detected (like something caught by
lockdep) it is a good idea to disable all tracing immediately, without
grabing any locks.

This patch adds ftrace_off_permanent that disables the tracers, function
tracing and ring buffers without a way to enable them again. This should
only be used when something serious has been detected.
Signed-off-by: Steven Rostedt <srostedt@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

include/linux/ftrace.h

@@ -257,6 +257,7 @@ extern int ftrace_dump_on_oops;
 
 extern void tracing_start(void);
 extern void tracing_stop(void);
+extern void ftrace_off_permanent(void);
 
 extern void
 ftrace_special(unsigned long arg1, unsigned long arg2, unsigned long arg3);
@@ -290,6 +291,7 @@ ftrace_printk(const char *fmt, ...) __attribute__ ((format (printf, 1, 0)));
 
 static inline void tracing_start(void) { }
 static inline void tracing_stop(void) { }
+static inline void ftrace_off_permanent(void) { }
 static inline int
 ftrace_printk(const char *fmt, ...)
 {

kernel/trace/trace.c

@@ -660,6 +660,21 @@ static void trace_init_cmdlines(void)
 static int trace_stop_count;
 static DEFINE_SPINLOCK(tracing_start_lock);
 
+/**
+ * ftrace_off_permanent - disable all ftrace code permanently
+ *
+ * This should only be called when a serious anomally has
+ * been detected.  This will turn off the function tracing,
+ * ring buffers, and other tracing utilites. It takes no
+ * locks and can be called from any context.
+ */
+void ftrace_off_permanent(void)
+{
+	tracing_disabled = 1;
+	ftrace_stop();
+	tracing_off_permanent();
+}
+
 /**
  * tracing_start - quick start of the tracer
  *