tracing: Erase irqsoff trace with empty write

BugLink: http://bugs.launchpad.net/bugs/1721550
commit 8dd33bcb7050dd6f8c1432732f930932c9d3a33e upstream.

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>
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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 8432d269779fe1aedb085c63ec1b3160d3c63563..8d7be6564151837a35faa216e4bc75350b06a29d 100644 (file)
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -3226,11 +3226,17 @@ 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) {