netdev - Re: [PATCH net] flow_dissector: disable preemption around BPF calls

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Message-ID: <20190513172527.GB16567@lakrids.cambridge.arm.com>
Date:   Mon, 13 May 2019 18:25:27 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     "David S . Miller" <davem@...emloft.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        netdev <netdev@...r.kernel.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        bpf <bpf@...r.kernel.org>, syzbot <syzkaller@...glegroups.com>,
        Petar Penkov <ppenkov@...gle.com>,
        Stanislav Fomichev <sdf@...gle.com>
Subject: Re: [PATCH net] flow_dissector: disable preemption around BPF calls

On Mon, May 13, 2019 at 10:20:19AM -0700, 'Eric Dumazet' via syzkaller wrote:
> On Mon, May 13, 2019 at 10:17 AM Mark Rutland <mark.rutland@....com> wrote:
> >
> > On Mon, May 13, 2019 at 09:38:55AM -0700, 'Eric Dumazet' via syzkaller wrote:
> > > Various things in eBPF really require us to disable preemption
> > > before running an eBPF program.
> >
> > Is that true for all eBPF uses? I note that we don't disable preemption
> > in the lib/test_bpf.c module, for example.
> >
> > If it's a general requirement, perhaps it's worth an assertion within
> > BPF_PROG_RUN()?
> 
> The assertion is already there :)
> 
> This is how syzbot triggered the report.

Ah! :)

I also see I'm wrong about test_bpf.c, so sorry for the noise on both
counts!

Thanks,
Mark.