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

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Date:   Mon, 13 May 2019 10:52:14 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Mark Rutland <mark.rutland@....com>,
        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>, 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 5/13/19 10:25 AM, Mark Rutland wrote:
> 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!

No worries, thanks for reviewing !