Re: [RFC PATCH 16/20] tools/rv: Add BPF monitors

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] tqueue monitor causes false positive invalid state transitions for tasks scheduling during do_exit().
--

commit 22065a19b365cd05306cad5f1def6f25a73bdc87
Author: Gabriele Monaco [off-list ref]

tools/rv: Add BPF monitors

This commit adds the code for 2 initial BPF monitors, both DA (the only
currently supported type): queue and nohz. It also integrates BPF monitor
building into the main rv Makefile.

[ ... ]

+SEC("tp_btf/sched_dequeue_tp")
+int BPF_PROG(handle_sched_dequeue, struct task_struct *tsk, int cpu)
+{
+	if (!(tsk->flags & PF_EXITING))
+		da_handle_start_event(tsk, sched_dequeue_tqueue);

[Severity: Medium]
Does skipping the dequeue event for exiting tasks here cause false positive
state transitions when the task is later enqueued?

If a task calls do_exit() (which sets PF_EXITING) and is preempted or sleeps
before reaching trace_sched_process_exit(), this logic skips the
sched_dequeue event. The state machine then incorrectly remains in the
"enqueued" state.

+	return 0;
+}
+
+SEC("tp_btf/sched_enqueue_tp")
+int BPF_PROG(handle_sched_enqueue, struct task_struct *tsk, int cpu)
+{
+	da_handle_event(tsk, sched_enqueue_tqueue);

[Severity: Medium]
When the exiting task is rescheduled, handle_sched_enqueue() unconditionally
processes the sched_enqueue event.

Since the corresponding dequeue event was skipped above, won't this un-paired
enqueue cause the monitor to transition to an invalid state, breaking the
intended functionality and flooding the trace logs with false positive
violations?

+	return 0;
+}

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260831090524.106845-1-gmonaco@redhat.com?part=16