tracing: Fix permissions for the buffer_percent file

This file defines both read and write operations, yet it is being
created as read-only. This means that it can't be written to without the
CAP_DAC_OVERRIDE capability. Fix the permissions to allow root to write
to it without the need to override DAC perms.

Link: https://lore.kernel.org/linux-trace-kernel/20230503140114.3280002-1-omosnace@redhat.com

Cc: stable@vger.kernel.org
Cc: Masami Hiramatsu <mhiramat@kernel.org>
Fixes: 03329f99 ("tracing: Add tracefs file buffer_percentage")
Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

kernel/trace/trace.c

@@ -9660,7 +9660,7 @@ init_tracer_tracefs(struct trace_array *tr, struct dentry *d_tracer)
 
 	tr->buffer_percent = 50;
 
-	trace_create_file("buffer_percent", TRACE_MODE_READ, d_tracer,
+	trace_create_file("buffer_percent", TRACE_MODE_WRITE, d_tracer,
 			tr, &buffer_percent_fops);
 
 	create_trace_options_dir(tr);