linux-kernel - [for-next][PATCH 11/12] ftrace,bug: Improve traceoff_on

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Date:   Mon, 01 Jun 2020 08:27:40 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     linux-kernel@...r.kernel.org
Cc:     Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>
Subject: [for-next][PATCH 11/12] ftrace,bug: Improve traceoff_on_warn

From: Peter Zijlstra <peterz@...radead.org>

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.

Link: https://lkml.kernel.org/r/20200528145240.GF706495@hirez.programming.kicks-ass.net

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.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;
-- 
2.26.2