netdev - Re: [PATCH v4 bpf-next 2/5] bpf: Introduce sleepable BPF programs

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Date:   Mon, 29 Jun 2020 20:03:36 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Andrii Nakryiko <andrii.nakryiko@...il.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Daniel Borkmann <daniel@...earbox.net>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Kernel Team <kernel-team@...com>
Subject: Re: [PATCH v4 bpf-next 2/5] bpf: Introduce sleepable BPF programs

On Mon, Jun 29, 2020 at 06:15:41PM -0700, Andrii Nakryiko wrote:
> >
> > +/* when rcu_read_lock_trace is held it means that some sleepable bpf program is
> > + * running. Those programs can use bpf arrays and preallocated hash maps. These
> > + * map types are waiting on programs to complete via
> > + * synchronize_rcu_tasks_trace();
> 
> Wanted to leave comment that "map types are waiting" is outdated after
> patch #1 and then recalled map-in-map complexities. So depending if
> I'm right or wrong regarding issue in patch #1, this would stay or has
> to be removed.

Good catch. The comment is outdated.
map-in-map is not supported with sleepable yet simply because I didn't have
time to think it through.

> > +                       verbose(env,
> > +                               "Sleepable programs can only use array and hash maps\n");
> 
> nit: message is a bit misleading. per-cpu array is also an array, yet
> is not supported.

yes. It's generic to avoid updating it too often. map-in-map is also not supported yet,
but it's a hash and array too.