linux-kernel - Re: [PATCH bpf-next] bpf: fix test_progs -j error with fentry/fexit tests

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Date:   Fri, 29 Jul 2022 15:43:57 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Song Liu <song@...nel.org>
Cc:     <bpf@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <live-patching@...r.kernel.org>, <daniel@...earbox.net>,
        <kernel-team@...com>, <jolsa@...nel.org>,
        Andrii Nakryiko <andrii@...nel.org>
Subject: Re: [PATCH bpf-next] bpf: fix test_progs -j error with fentry/fexit
 tests

On Fri, 29 Jul 2022 12:41:06 -0700
Song Liu <song@...nel.org> 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.
>