[patch V6 03/37] nmi, tracing: Provide nmi_enter/exit_notrace()

[Thomas Gleixner <tglx@linutronix.de>]

To fully isolate #DB and #BP from instrumentable code it's necessary to
avoid invoking the hardware latency tracer on nmi_enter/exit().

Provide nmi_enter/exit() variants which are not invoking the hardware
latency tracer. That allows to put calls explicitely into the call sites
outside of the kprobe handling.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

---
 include/linux/hardirq.h |   23 +++++++++++++++++++++--
 1 file changed, 21 insertions(+), 2 deletions(-)

--- a/include/linux/hardirq.h
+++ b/include/linux/hardirq.h
@@ -76,8 +76,16 @@ extern void irq_exit(void);
 
 /*
  * nmi_enter() can nest up to 15 times; see NMI_BITS.
+ *
+ * ftrace_count_nmi() only increments a counter and is noinstr safe so it
+ * can be invoked in nmi_enter_notrace(). ftrace_nmi_handler_enter/exit()
+ * does time stamping and will be invoked in the actual NMI handling after
+ * an instrumentable section has been reached.
+ *
+ * nmi_enter/exit() still calls into the tracer so existing callers
+ * wont break.
  */
-#define nmi_enter()						\
+#define nmi_enter_notrace()					\
 	do {							\
 		arch_nmi_enter();				\
 		printk_nmi_enter();				\
@@ -87,10 +95,15 @@ extern void irq_exit(void);
 		rcu_nmi_enter();				\
 		lockdep_hardirq_enter();			\
 		ftrace_count_nmi();				\
+	} while (0)
+
+#define nmi_enter()						\
+	do {							\
+		nmi_enter_notrace();				\
 		ftrace_nmi_handler_enter();			\
 	} while (0)
 
-#define nmi_exit()						\
+#define nmi_exit_notrace()					\
 	do {							\
 		ftrace_nmi_handler_exit();			\
 		lockdep_hardirq_exit();				\
@@ -102,4 +115,10 @@ extern void irq_exit(void);
 		arch_nmi_exit();				\
 	} while (0)
 
+#define nmi_exit()						\
+	do {							\
+		ftrace_nmi_handler_exit();			\
+		nmi_exit_notrace();				\
+	} while (0)
+
 #endif /* LINUX_HARDIRQ_H */