tracing: Fix to set write permission to per-cpu buffer_size_kb

Since the per-cpu buffer_size_kb file is writable for changing
per-cpu ring buffer size, the file should have the write access
permission.

Cc: stable@vger.kernel.org
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Link: https://patch.msgid.link/177071301597.2293046.11683339475076917920.stgit@mhiramat.tok.corp.google.com
Fixes: 21ccc9c ("tracing: Disable "other" permission bits in the tracefs files")
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

Author: mhiramat

kernel/trace/trace.c

@@ -8613,7 +8613,7 @@ tracing_init_tracefs_percpu(struct trace_array *tr, long cpu)
 	trace_create_cpu_file("stats", TRACE_MODE_READ, d_cpu,
 				tr, cpu, &tracing_stats_fops);
 
-	trace_create_cpu_file("buffer_size_kb", TRACE_MODE_READ, d_cpu,
+	trace_create_cpu_file("buffer_size_kb", TRACE_MODE_WRITE, d_cpu,
 				tr, cpu, &tracing_entries_fops);
 
 	if (tr->range_addr_start)