From: Martin Lau <kafai@fb.com>
To: Wei Wang <weiwan@google.com>
Cc: David Ahern <dsahern@gmail.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: Wed, 16 Oct 2019 06:35:15 +0000 [thread overview]
Message-ID: <20191016063512.fnq7e74hrnqdsj7f@kafai-mbp.dhcp.thefacebook.com> (raw)
In-Reply-To: <CAEA6p_A_zB0uLn34UeCpXOSQZiOsPFfcfvDtmNZWrks6PCj0=g@mail.gmail.com>
On Tue, Oct 15, 2019 at 09:42:49AM -0700, Wei Wang wrote:
> 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.
Exactly :) If no re-create, dst_dev_put() can be avoided.
The root cause is not really related to the global NS rt_genid.
A granular rt_genid may help to reduce the race on dst_dev_put()
but it will still happen. (that aside, improving the NS rt_genid
would still be great).
Thinking more about it, this issue should not be limited to input.
I think you fix is right.
>
> >
> > 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.
next prev parent reply other threads:[~2019-10-16 6:35 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
2019-10-16 6:35 ` Martin Lau [this message]
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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