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Date:   Wed, 1 Jul 2020 21:03:00 +0200
From:   KP Singh <>
To:     Alexei Starovoitov <>
Cc:     Daniel Borkmann <>,
        "David S. Miller" <>,
        "Paul E. McKenney" <>,
        Network Development <>,
        bpf <>, Kernel Team <>
Subject: Re: [PATCH v5 bpf-next 2/5] bpf: Introduce sleepable BPF programs

On Wed, Jul 1, 2020 at 5:14 PM Alexei Starovoitov
<> wrote:
> On Wed, Jul 1, 2020 at 2:17 AM Daniel Borkmann <> 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.

I found one other hook, file_send_sigiotask, which mentions
"Note that this hook is sometimes called from interrupt." So I think
we should add it to the list as well.

Given some more due diligence done here
and Daniel's proposal of adding __might_sleep() to
the __bpf_prog_enter_sleepable() we should be able to
iterate on finding other non-sleepable hooks (if they exist)
and eventually augmenting the LSM_HOOK macro for a
more structured way to store this information.

- KP

> 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.

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