[PATCH v2] kprobes: Fix kill kprobe which has been marked as gone

[Muchun Song]

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: e8386a0cb22f ("kprobes: support probing module __exit function")
Signed-off-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
Co-developed-by: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
Signed-off-by: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
Acked-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
---
changelogs in v2:
 1. Add a WARN_ON_ONCE in the kill_kprobe() to catch incorrect use of it.
 2. Update 'Fixes' tag in the commmit log.

 kernel/kprobes.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index d36e2b017588..9348b0c36ae0 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -2143,6 +2143,9 @@ 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)) {
 		/*
@@ -2422,7 +2425,10 @@ 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))) {
@@ -2439,6 +2445,7 @@ static int kprobes_module_callback(struct notifier_block *nb,
 				 */
 				kill_kprobe(p);
 			}
+		}
 	}
 	if (val == MODULE_STATE_GOING)
 		remove_module_kprobe_blacklist(mod);
-- 
2.11.0