From 8dd33bcb7050dd6f8c1432732f930932c9d3a33e Mon Sep 17 00:00:00 2001
From: Bo Yan <byan@nvidia.com>
Date: Mon, 18 Sep 2017 10:03:35 -0700
Subject: [PATCH] tracing: Erase irqsoff trace with empty write
Git-commit: 8dd33bcb7050dd6f8c1432732f930932c9d3a33e
Patch-mainline: v4.14-rc2
References: bsc#1117189

One convenient way to erase trace is "echo > trace". However, this
is currently broken if the current tracer is irqsoff tracer. This
is because irqsoff tracer use max_buffer as the default trace
buffer.

Set the max_buffer as the one to be cleared when it's the trace
buffer currently in use.

Link: http://lkml.kernel.org/r/1505754215-29411-1-git-send-email-byan@nvidia.com

Cc: <mingo@redhat.com>
Cc: stable@vger.kernel.org
Fixes: 4acd4d00f ("tracing: give easy way to clear trace buffer")
Signed-off-by: Bo Yan <byan@nvidia.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Acked-by: Petr Mladek <pmladek@suse.com>

---
 kernel/trace/trace.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 5360b7aec57a..a7fb136da891 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -4020,11 +4020,17 @@ static int tracing_open(struct inode *inode, struct file *file)
 	/* If this file was open for write, then erase contents */
 	if ((file->f_mode & FMODE_WRITE) && (file->f_flags & O_TRUNC)) {
 		int cpu = tracing_get_cpu(inode);
+		struct trace_buffer *trace_buf = &tr->trace_buffer;
+
+#ifdef CONFIG_TRACER_MAX_TRACE
+		if (tr->current_trace->print_max)
+			trace_buf = &tr->max_buffer;
+#endif
 
 		if (cpu == RING_BUFFER_ALL_CPUS)
-			tracing_reset_online_cpus(&tr->trace_buffer);
+			tracing_reset_online_cpus(trace_buf);
 		else
-			tracing_reset(&tr->trace_buffer, cpu);
+			tracing_reset(trace_buf, cpu);
 	}
 
 	if (file->f_mode & FMODE_READ) {
-- 
2.13.7