Re: net: suspicious RCU usage in nf_hook

[Cong Wang]

On Wed, Feb 1, 2017 at 3:59 PM, Eric Dumazet <eric.dumazet@xxxxxxxxx> wrote:
> On Wed, 2017-02-01 at 15:48 -0800, Eric Dumazet wrote:
>> On Wed, Feb 1, 2017 at 3:29 PM, Cong Wang <xiyou.wangcong@xxxxxxxxx> wrote:
>>
>> > Not sure if it is better. The difference is caught up in net_enable_timestamp(),
>> > which is called setsockopt() path and sk_clone() path, so we could be
>> > in netstamp_needed state for a long time too until user-space exercises
>> > these paths.
>> >
>> > I am feeling we probably need to get rid of netstamp_needed_deferred,
>> > and simply defer the whole static_key_slow_dec(), like the attached patch
>> > (compile only).
>> >
>> > What do you think?
>>
>> I think we need to keep the atomic.
>>
>> If two cpus call net_disable_timestamp() roughly at the same time, the
>> work will be scheduled once.

Good point! Yeah, the same work will not be schedule twice.

>
> Updated patch (but not tested yet)

I can't think out a better way to fix this. I expect jump_label to provide
an API for this, but it doesn't, static_key_slow_dec_deferred()
is just for batching. Probably we should introduce one to avoid these
ugly #ifdef HAVE_JUMP_LABEL here, but that is a -next material.

So, please feel free to send it formally.

Thanks.