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From: Cong Wang <xiyou.wangcong@gmail.com>
To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Eric Dumazet <edumazet@google.com>,
	Dmitry Vyukov <dvyukov@google.com>,
	David Miller <davem@davemloft.net>,
	Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>,
	James Morris <jmorris@namei.org>,
	Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
	Patrick McHardy <kaber@trash.net>,
	netdev <netdev@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Pablo Neira Ayuso <pablo@netfilter.org>,
	netfilter-devel@vger.kernel.org,
	syzkaller <syzkaller@googlegroups.com>
Subject: Re: net: suspicious RCU usage in nf_hook
Date: Thu, 2 Feb 2017 10:01:02 -0800	[thread overview]
Message-ID: <CAM_iQpUVma3R7wGJ8T8FWyCpU9joiGM+8LSPMcV2xpJLiRD-pw@mail.gmail.com> (raw)
In-Reply-To: <1485993583.6360.172.camel@edumazet-glaptop3.roam.corp.google.com>

On Wed, Feb 1, 2017 at 3:59 PM, Eric Dumazet <eric.dumazet@gmail.com> 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@gmail.com> 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.

  reply	other threads:[~2017-02-02 18:01 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-01-27 21:15 net: suspicious RCU usage in nf_hook Dmitry Vyukov
2017-01-27 23:22 ` Cong Wang
2017-01-27 23:30   ` Cong Wang
2017-01-27 23:35 ` Eric Dumazet
2017-01-28  1:00   ` Cong Wang
2017-01-28  1:31     ` Eric Dumazet
2017-01-31  6:19       ` Cong Wang
2017-01-31 15:44         ` Eric Dumazet
2017-02-01 20:51           ` Cong Wang
2017-02-01 21:16             ` Eric Dumazet
2017-02-01 21:22               ` Eric Dumazet
2017-02-01 23:29               ` Cong Wang
2017-02-01 23:48                 ` Eric Dumazet
2017-02-01 23:59                   ` Eric Dumazet
2017-02-02 18:01                     ` Cong Wang [this message]
2017-02-02 18:31                       ` [PATCH net] net: use a work queue to defer net_disable_timestamp() work Eric Dumazet
2017-02-03 21:18                         ` David Miller

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