kprobes: fix kill kprobe which has been marked as gone

If a kprobe is marked as gone, we should not kill it again.  Otherwise, we
can disarm the kprobe more than once.  In that case, the statistics of
kprobe_ftrace_enabled can unbalance which can lead to that kprobe do not
work.

Fixes: e8386a0 ("kprobes: support probing module __exit function")
Co-developed-by: Chengming Zhou <[email protected]>
Signed-off-by: Muchun Song <[email protected]>
Signed-off-by: Chengming Zhou <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Acked-by: Masami Hiramatsu <[email protected]>
Cc: "Naveen N . Rao" <[email protected]>
Cc: Anil S Keshavamurthy <[email protected]>
Cc: David S. Miller <[email protected]>
Cc: Song Liu <[email protected]>
Cc: Steven Rostedt <[email protected]>
Cc: <[email protected]>
Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Linus Torvalds <[email protected]>

kernel/kprobes.c

@@ -2140,6 +2140,9 @@ static void kill_kprobe(struct kprobe *p)
 
 	lockdep_assert_held(&kprobe_mutex);
 
+	if (WARN_ON_ONCE(kprobe_gone(p)))
+		return;
+
 	p->flags |= KPROBE_FLAG_GONE;
 	if (kprobe_aggrprobe(p)) {
 		/*
@@ -2419,7 +2422,10 @@ static int kprobes_module_callback(struct notifier_block *nb,
 	mutex_lock(&kprobe_mutex);
 	for (i = 0; i < KPROBE_TABLE_SIZE; i++) {
 		head = &kprobe_table[i];
-		hlist_for_each_entry(p, head, hlist)
+		hlist_for_each_entry(p, head, hlist) {
+			if (kprobe_gone(p))
+				continue;
+
 			if (within_module_init((unsigned long)p->addr, mod) ||
 			    (checkcore &&
 			     within_module_core((unsigned long)p->addr, mod))) {
@@ -2436,6 +2442,7 @@ static int kprobes_module_callback(struct notifier_block *nb,
 				 */
 				kill_kprobe(p);
 			}
+		}
 	}
 	if (val == MODULE_STATE_GOING)
 		remove_module_kprobe_blacklist(mod);