lib/error-inject: traverse list with mutex

Traversing list without mutex in get_injectable_error_type will
race with the following code:
list_del_init(&ent->list)
kfree(ent)
in module_unload_ei_list. So fix that.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: wuchi <[e-mail]>
Cc: Masami Hiramatsu (Google) <[e-mail]>
Cc: Martin KaFai Lau <[e-mail]>
Cc: Song Liu <[e-mail]>
Cc: Yonghong Song <[e-mail]>
Cc: John Fastabend <[e-mail]>
Cc: KP Singh <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

lib/error-inject.c

···
 int get_injectable_error_type(unsigned long addr)
 {
 	struct ei_entry *ent;
+	int ei_type = EI_ETYPE_NONE;
 
+	mutex_lock(&ei_mutex);
 	list_for_each_entry(ent, &error_injection_list, list) {
-		if (addr >= ent->start_addr && addr < ent->end_addr)
-			return ent->etype;
+		if (addr >= ent->start_addr && addr < ent->end_addr) {
+			ei_type = ent->etype;
+			break;
+		}
 	}
-	return EI_ETYPE_NONE;
+	mutex_unlock(&ei_mutex);
+
+	return ei_type;
 }
 
 /*