kprobes: Fix to protect kick_kprobe_optimizer() by kprobe_mutex

In kprobe_optimizer() kick_kprobe_optimizer() is called
without kprobe_mutex, but this can race with other caller
which is protected by kprobe_mutex.

To fix that, expand kprobe_mutex protected area to protect
kick_kprobe_optimizer() call.

Link: http://lkml.kernel.org/r/158927057586.27680.5036330063955940456.stgit@devnote2

Fixes: cd7ebe2 ("kprobes: Use text_poke_smp_batch for optimizing")
Cc: Ingo Molnar <[email protected]>
Cc: "Gustavo A . R . Silva" <[email protected]>
Cc: Anders Roxell <[email protected]>
Cc: "Naveen N . Rao" <[email protected]>
Cc: Anil S Keshavamurthy <[email protected]>
Cc: David Miller <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Ziqian SUN <[email protected]>
Cc: [email protected]
Signed-off-by: Masami Hiramatsu <[email protected]>
Signed-off-by: Steven Rostedt (VMware) <[email protected]>

kernel/kprobes.c

@@ -592,11 +592,12 @@ static void kprobe_optimizer(struct work_struct *work)
 	mutex_unlock(&module_mutex);
 	mutex_unlock(&text_mutex);
 	cpus_read_unlock();
-	mutex_unlock(&kprobe_mutex);
 
 	/* Step 5: Kick optimizer again if needed */
 	if (!list_empty(&optimizing_list) || !list_empty(&unoptimizing_list))
 		kick_kprobe_optimizer();
+
+	mutex_unlock(&kprobe_mutex);
 }
 
 /* Wait for completing optimization and unoptimization */