netdev - Re: [PATCH v5 bpf-next 2/5] bpf: Introduce sleepable BPF programs

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Date:   Wed, 1 Jul 2020 08:14:41 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     "David S. Miller" <davem@...emloft.net>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Network Development <netdev@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>, Kernel Team <kernel-team@...com>
Subject: Re: [PATCH v5 bpf-next 2/5] bpf: Introduce sleepable BPF programs

On Wed, Jul 1, 2020 at 2:17 AM Daniel Borkmann <daniel@...earbox.net> wrote:
> ("bpf: Replace cant_sleep() with cant_migrate()"). So perhaps one way to catch
> bugs for sleepable progs is to add a __might_sleep() into __bpf_prog_enter_sleepable()

that's a good idea.

> in order to trigger the assertion generally for DEBUG_ATOMIC_SLEEP configured
> kernels when we're in non-sleepable sections? Still not perfect since the code
> needs to be exercised first but better than nothing at all.
>
> >> What about others like security_sock_rcv_skb() for example which could be
> >> bh_lock_sock()'ed (or, generally hooks running in softirq context)?
> >
> > ahh. it's in running in bh at that point? then it should be added to blacklist.
>
> Yep.

I'm assuming KP will take care of it soon.
If not I'll come back to this set some time in August.

In the meantime I've pushed patch 1 that removes redundant sync_rcu to bpf-next,
since it's independent and it benefits from being in the tree as much
as possible.