On Fri, 29 Jul 2022 12:41:06 -0700
Song Liu <song@xxxxxxxxxx> wrote:
> Then multiple threads are attaching/detaching fentry/fexit programs to
"When multiple threads"?
-- Steve
> the same trampoline, we may call register_fentry on the same trampoline
> twice: register_fentry(), unregister_fentry(), then register_fentry again.
> This causes ftrace_set_filter_ip() for the same ip on tr->fops twice,
> which leaves duplicated ip in tr->fops. The extra ip is not cleaned up
> properly on unregister and thus causes failures with further register in
> register_ftrace_direct_multi():
>
> register_ftrace_direct_multi()
> {
> ...
> for (i = 0; i < size; i++) {
> hlist_for_each_entry(entry, &hash->buckets[i], hlist) {
> if (ftrace_find_rec_direct(entry->ip))
> goto out_unlock;
> }
> }
> ...
> }
>
> This can be triggered with parallel fentry/fexit tests with test_progs:
>
> ./test_progs -t fentry,fexit -j
>
> Fix this by resetting tr->fops in ftrace_set_filter_ip(), so that there
> will never be duplicated entries in tr->fops.
>
