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From: Wei Wang <weiwan@google.com>
To: David Ahern <dsahern@gmail.com>
Cc: Martin Lau <kafai@fb.com>, Ido Schimmel <idosch@idosch.org>,
	Jesse Hathaway <jesse@mbuki-mvuki.org>,
	Linux Kernel Network Developers <netdev@vger.kernel.org>
Subject: Re: Race condition in route lookup
Date: Tue, 15 Oct 2019 09:42:49 -0700	[thread overview]
Message-ID: <CAEA6p_A_zB0uLn34UeCpXOSQZiOsPFfcfvDtmNZWrks6PCj0=g@mail.gmail.com> (raw)
In-Reply-To: <9d4dd279-b20a-e333-2dd6-fe2901e67bce@gmail.com>

On Tue, Oct 15, 2019 at 7:45 AM David Ahern <dsahern@gmail.com> wrote:
>
> On 10/14/19 1:26 PM, Martin Lau wrote:
> >
> > AFAICT, even for the route that are affected by fib6_update_sernum_upto_root(),
> > I don't see the RTF_PCPU route is re-created.  v6 sk does
> > dst_check() => re-lookup the fib6 =>
> > found the same RTF_PCPU (but does not re-create it) =>
> > update the sk with new cookie in ip6_dst_store()
> >
Hmm... That is a good point. Why does v4 need to recreate the dst
cache even though the route itself is not changed?
Now that I think about it, I agree with Martin's previous comment: it
probably is because v4 code does not cache rt->rt_genid into the
socket and every user of the rt is sharing the same rt_genid stored in
the route itself.

>
> That's fine. The pcpu cache is per nexthop (fib6_nh) for a specific
> gateway/device.
>
> The invalidate forces another lookup for the intended destination after
> the change to the fib. If the lookup resolves to the same fib entry and
> nexthop, then re-using the same cached dst/rt6_info is ok.

  reply	other threads:[~2019-10-15 16:43 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-09 16:00 Race condition in route lookup Jesse Hathaway
2019-10-10  8:31 ` Ido Schimmel
2019-10-10  8:46   ` Ido Schimmel
2019-10-11 14:36   ` Jesse Hathaway
2019-10-11 15:42     ` Ido Schimmel
2019-10-11 16:09       ` Jesse Hathaway
2019-10-11 17:54       ` Wei Wang
2019-10-11 18:17         ` Ido Schimmel
2019-10-11 18:25           ` Ido Schimmel
2019-10-11 18:47             ` Wei Wang
2019-10-11 18:52               ` Ido Schimmel
2019-10-11 21:01                 ` Jesse Hathaway
2019-10-11 21:27                 ` David Ahern
2019-10-12  6:56         ` Martin Lau
2019-10-14  0:23           ` Wei Wang
2019-10-14 17:26             ` Martin Lau
2019-10-15 14:45               ` David Ahern
2019-10-15 16:42                 ` Wei Wang [this message]
2019-10-16  6:35                   ` Martin Lau
2019-10-15 14:29         ` Jesse Hathaway
2019-10-15 16:44           ` Wei Wang
2019-10-16  6:39             ` Martin Lau
2019-10-16 16:35               ` Wei Wang

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