linux-kernel - Re: net/tcp: warning in tcp_try_coalesce/skb_try

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Date:   Thu, 2 Feb 2017 18:34:05 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     Eric Dumazet <edumazet@...gle.com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        "David S. Miller" <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        James Morris <jmorris@...ei.org>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Patrick McHardy <kaber@...sh.net>,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Kostya Serebryany <kcc@...gle.com>,
        syzkaller <syzkaller@...glegroups.com>
Subject: Re: net/tcp: warning in tcp_try_coalesce/skb_try_coalesce

On Thu, Feb 2, 2017 at 3:03 PM, Dmitry Vyukov <dvyukov@...gle.com> wrote:
> On Thu, Feb 2, 2017 at 2:56 PM, Dmitry Vyukov <dvyukov@...gle.com> wrote:
>> On Thu, Feb 2, 2017 at 2:40 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
>>> On Thu, 2017-02-02 at 13:59 +0100, Dmitry Vyukov wrote:
>>>
>>>>
>>>> Right, I can confirm that this is not happening on net-next tip
>>>> (62e13097c46c69dbd7544ab2cd585ccf48f360a4).
>>>> I reproduced it on a random month old commit on net-next, though
>>>> (23a8ed4a624324dc696c328f09bd502c4a3816f0). Let's consider that this
>>>> is accidentally fixed by something in that range.
>>>
>>> This also might depend on the .config
>>>
>>> I tried 23a8ed4a624324dc696c328f09bd502c4a3816f0 and could not trigger
>>> the warning .
>>
>>
>> I've attached my config.
>> But I've tried with the same config on both revisions.
>>
>> Well, there is also a chance that the bug is not fixed, but requires
>> slightly different reproducer after some changes.
>
> Hummm....
>
> My config includes KASAN+KCOV and I use gcc version 7.0.0 20161208
> (experimental) (GCC).
> I've now tried to turn off KASAN+KCOV and compiled with my stock
> 4.8.4, and this did _not_ trigger the warning on
> 23a8ed4a624324dc696c328f09bd502c4a3816f0.

Wait, I managed to reproduce it on
23a8ed4a624324dc696c328f09bd502c4a3816f0 without KASAN/KCOV with
4.8.4. It just required more time (like several minutes).

So I would expect that you should be able to reproduce it as well.
I've attached my new config.

Download attachment ".config" of type "application/octet-stream" (116187 bytes)