From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: David Miller <davem@davemloft.net>,
Yuchung Cheng <ycheng@google.com>,
Oleksandr Natalenko <oleksandr@natalenko.name>,
Roman Gushchin <guro@fb.com>, netdev <netdev@vger.kernel.org>,
Neal Cardwell <ncardwell@google.com>,
Lawrence Brakmo <brakmo@fb.com>
Subject: Re: [PATCH net] tcp: fix tcp_mtu_probe() vs highest_sack
Date: Mon, 30 Oct 2017 23:30:19 -0700 [thread overview]
Message-ID: <20171031063018.ezzfd6hitd535lar@ast-mbp> (raw)
In-Reply-To: <1509430902.3828.15.camel@edumazet-glaptop3.roam.corp.google.com>
On Mon, Oct 30, 2017 at 11:21:42PM -0700, Eric Dumazet wrote:
> On Mon, 2017-10-30 at 23:17 -0700, Alexei Starovoitov wrote:
> > On Mon, Oct 30, 2017 at 11:08:20PM -0700, Eric Dumazet wrote:
> > > From: Eric Dumazet <edumazet@google.com>
> > >
> > > Based on SNMP values provided by Roman, Yuchung made the observation
> > > that some crashes in tcp_sacktag_walk() might be caused by MTU probing.
> > >
> > > Looking at tcp_mtu_probe(), I found that when a new skb was placed
> > > in front of the write queue, we were not updating tcp highest sack.
> > >
> > > If one skb is freed because all its content was copied to the new skb
> > > (for MTU probing), then tp->highest_sack could point to a now freed skb.
> > >
> > > Bad things would then happen, including infinite loops.
> > >
> > > This patch renames tcp_highest_sack_combine() and uses it
> > > from tcp_mtu_probe() to fix the bug.
> > >
> > > Note that I also removed one test against tp->sacked_out,
> > > since we want to replace tp->highest_sack regardless of whatever
> > > condition, since keeping a stale pointer to freed skb is a recipe
> > > for disaster.
> > >
> > > Fixes: a47e5a988a57 ("[TCP]: Convert highest_sack to sk_buff to allow direct access")
> > > Signed-off-by: Eric Dumazet <edumazet@google.com>
> > > Reported-by: Alexei Starovoitov <alexei.starovoitov@gmail.com>
> > > Reported-by: Roman Gushchin <guro@fb.com>
> > > Reported-by: Oleksandr Natalenko <oleksandr@natalenko.name>
> >
> > Thanks!
> >
> > Acked-by: Alexei Starovoitov <ast@kernel.org>
> >
> > wow. a bug from 2007.
> > Any idea why it only started to bite us in 4.11 ?
> >
> > It's not trivial for us to reproduce it, but we will definitely
> > test the patch as soon as we can.
> > Do you have packet drill test or something for easy repro?
>
> I tried to cook a packetdrill test but could not trigger the issue.
>
> When have you started to enable mtu probing ?
for some time. somehow 4.6 based kernel didn't trigger it.
May be it's a different bug still...
next prev parent reply other threads:[~2017-10-31 6:30 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-09-21 1:46 [REGRESSION] Warning in tcp_fastretrans_alert() of net/ipv4/tcp_input.c Roman Gushchin
2017-09-21 17:07 ` Yuchung Cheng
[not found] ` <CAK6E8=cGF+xKiixRVvA=3PVPA7OQta9hVLTgCbKgvYf3e9Eu-A@mail.gmail.com>
2017-09-26 13:10 ` Roman Gushchin
2017-09-27 0:12 ` Yuchung Cheng
2017-09-27 0:18 ` Yuchung Cheng
2017-09-28 8:14 ` Oleksandr Natalenko
2017-09-28 23:36 ` Yuchung Cheng
2017-10-26 2:07 ` Alexei Starovoitov
2017-10-26 5:37 ` Yuchung Cheng
2017-10-27 20:38 ` Eric Dumazet
2017-10-31 6:08 ` [PATCH net] tcp: fix tcp_mtu_probe() vs highest_sack Eric Dumazet
2017-10-31 6:17 ` Alexei Starovoitov
2017-10-31 6:21 ` Eric Dumazet
2017-10-31 6:30 ` Alexei Starovoitov [this message]
2017-11-01 5:50 ` Yuchung Cheng
2017-10-31 13:51 ` Neal Cardwell
2017-11-01 12:20 ` David Miller
2017-11-03 18:22 ` Oleksandr Natalenko
2017-11-03 21:31 ` Eric Dumazet
2017-11-06 22:27 ` [REGRESSION] Warning in tcp_fastretrans_alert() of net/ipv4/tcp_input.c Yuchung Cheng
2017-11-10 13:15 ` Oleksandr Natalenko
2017-11-10 13:40 ` Oleksandr Natalenko
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