tracing: Erase irqsoff trace with empty write

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>

1 files 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) {