Re: [PATCH bpf-next v4 2/6] netfilter: bpf: Support BPF_F_NETFILTER_IP_DEFRAG in netfilter link

[Alexei Starovoitov]

On Wed, Jul 12, 2023 at 4:44 PM Daniel Xu <dxu@xxxxxxxxx> wrote:
> +#if IS_ENABLED(CONFIG_NF_DEFRAG_IPV6)
> +       case NFPROTO_IPV6:
> +               rcu_read_lock();
> +               v6_hook = rcu_dereference(nf_defrag_v6_hook);
> +               if (!v6_hook) {
> +                       rcu_read_unlock();
> +                       err = request_module("nf_defrag_ipv6");
> +                       if (err)
> +                               return err < 0 ? err : -EINVAL;
> +
> +                       rcu_read_lock();
> +                       v6_hook = rcu_dereference(nf_defrag_v6_hook);
> +                       if (!v6_hook) {
> +                               WARN_ONCE(1, "nf_defrag_ipv6_hooks bad registration");
> +                               err = -ENOENT;
> +                               goto out_v6;
> +                       }
> +               }
> +
> +               err = v6_hook->enable(link->net);

I was about to apply, but luckily caught this issue in my local test:

[   18.462448] BUG: sleeping function called from invalid context at
kernel/locking/mutex.c:283
[   18.463238] in_atomic(): 0, irqs_disabled(): 0, non_block: 0, pid:
2042, name: test_progs
[   18.463927] preempt_count: 0, expected: 0
[   18.464249] RCU nest depth: 1, expected: 0
[   18.464631] CPU: 15 PID: 2042 Comm: test_progs Tainted: G
O       6.4.0-04319-g6f6ec4fa00dc #4896
[   18.465480] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996),
BIOS rel-1.12.0-59-gc9ba5276e321-prebuilt.qemu.org 04/01/2014
[   18.466531] Call Trace:
[   18.466767]  <TASK>
[   18.466975]  dump_stack_lvl+0x32/0x40
[   18.467325]  __might_resched+0x129/0x180
[   18.467691]  mutex_lock+0x1a/0x40
[   18.468057]  nf_defrag_ipv4_enable+0x16/0x70
[   18.468467]  bpf_nf_link_attach+0x141/0x300
[   18.468856]  __sys_bpf+0x133e/0x26d0

You cannot call mutex under rcu_read_lock.

Please make sure you have all kernel debug flags on in your testing.