clocksource: clocksource_select must be called with mutex locked

The callers of clocksource_select must hold clocksource_mutex to
protect the clocksource_list.

Signed-off-by: Thomas Gleixner <[e-mail]>
LKML-Reference: <new-submission>
Cc: Martin Schwidefsky <[e-mail]>

kernel/time/clocksource.c

···
 static int __init clocksource_done_booting(void)
 {
 	finished_booting = 1;
+	mutex_lock(&clocksource_mutex);
 	clocksource_select();
+	mutex_unlock(&clocksource_mutex);
 	return 0;
 }
 fs_initcall(clocksource_done_booting);