[PATCH v2 3/3] kprobes: Arm reused optprobe on cooling list

[Mani Tofigh via B4 Relay]

From: Mani Tofigh <mt4022@xxxxxxxxxxxx>

A new probe that reuses an unused probe still on a cooling list doesn't
fire.  reuse_unused_kprobe() clears DISABLED, so register_aggr_kprobe()
doesn't arm it and the probe has no int3 until it's optimized again, or
ever if it can't be (e.g., it has a post_handler).

Keep a reused cooling probe disabled instead, so register_aggr_kprobe()
arms it if the new probe is enabled, or enable_kprobe() does it later.
The probe is then still unused when add_new_kprobe() force-unoptimizes
it for a new probe with a post_handler, which would unhash it and queue
it for freeing.  Skip that since a cooling probe is already unoptimized.
With the fix, the new probe fires.

Fixes: 06e0d3b89da1 ("kprobes: Make optprobe optimizer multi-generational and asynchronous")
Suggested-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
Signed-off-by: Mani Tofigh <mt4022@xxxxxxxxxxxx>
---
Changes in v2:
- Keep a reused cooling probe disabled so register_aggr_kprobe() arms it
  only for an enabled new probe (Masami, Sashiko)
- Skip the forced unoptimization in add_new_kprobe() for a cooling probe
---
 kernel/kprobes.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/kernel/kprobes.c b/kernel/kprobes.c
index 099a38ca146a..5f8ce6892bd1 100644
--- a/kernel/kprobes.c
+++ b/kernel/kprobes.c
@@ -1059,6 +1059,10 @@ static int reuse_unused_kprobe(struct kprobe *ap)
 	 */
 	op = container_of(ap, struct optimized_kprobe, kp);
 	WARN_ON_ONCE(list_empty(&op->list));
+	/* Already disarmed, the caller arms it only for an enabled probe */
+	if (optprobe_queued_cooling(op))
+		return 0;
+
 	/* Enable the probe again */
 	ap->flags &= ~KPROBE_FLAG_DISABLED;
 	/* Optimize it again. (remove from 'op->list') */
@@ -1571,7 +1575,8 @@ void kprobe_busy_end(void)
 /* Add the new probe to 'ap->list'. */
 static int add_new_kprobe(struct kprobe *ap, struct kprobe *p)
 {
-	if (p->post_handler)
+	/* A reused cooling probe is already unoptimized */
+	if (p->post_handler && !kprobe_unused(ap))
 		unoptimize_kprobe(ap, true);	/* Fall back to normal kprobe */
 
 	list_add_rcu(&p->list, &ap->list);

-- 
2.53.0