[PATCH] ftrace,bug: Improve traceoff_on_warn

[Peter Zijlstra <peterz@infradead.org>]

Hai,

While doing some tracing, I found a huge portion of the per-cpu buffer
was taken by printk/serial output because we're disabling the trace far
too late (after printing the CUT string).

Improve matters for architectures that have GENERIC_BUG + _BUG_FLAGS by
killing the tracer in the exception handler before printing anything
much.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
 lib/bug.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/lib/bug.c b/lib/bug.c
index 8c98af0bf585..7103440c0ee1 100644
--- a/lib/bug.c
+++ b/lib/bug.c
@@ -47,6 +47,7 @@
 #include <linux/bug.h>
 #include <linux/sched.h>
 #include <linux/rculist.h>
+#include <linux/ftrace.h>
 
 extern struct bug_entry __start___bug_table[], __stop___bug_table[];
 
@@ -153,6 +154,8 @@ enum bug_trap_type report_bug(unsigned long bugaddr, struct pt_regs *regs)
 	if (!bug)
 		return BUG_TRAP_TYPE_NONE;
 
+	disable_trace_on_warning();
+
 	file = NULL;
 	line = 0;
 	warning = 0;