linux-kernel - Re: [lkp-robot] [x86/refcount] b631e535c6: WARNING:at_net/netlink/af_netlink.c:#netlink_sock

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Message-ID: <20170727133424.nk45rutdleyirva2@ishxps>
Date:   Thu, 27 Jul 2017 16:34:24 +0300
From:   Hans Liljestrand <liljestrandh@...il.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     "Reshetova, Elena" <elena.reshetova@...el.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>, LKP <lkp@...org>
Subject: Re: [lkp-robot] [x86/refcount] b631e535c6:
 WARNING:at_net/netlink/af_netlink.c:#netlink_sock_destruct

On Tue, Jul 25, 2017 at 11:38:30AM -0700, Kees Cook wrote:
>On Tue, Jul 25, 2017 at 3:43 AM, Hans Liljestrand
><liljestrandh@...il.com> wrote:
>> On Mon, Jul 24, 2017 at 08:21:16PM -0700, Kees Cook wrote:
>>>
>>> On Mon, Jul 24, 2017 at 6:03 AM, Hans Liljestrand
>>> <liljestrandh@...il.com> wrote:
>>>>
>>>> On Sun, Jul 23, 2017 at 08:52:53PM -0700, Kees Cook wrote:
>>>>>
>>>>>
>>>>> Is 14afee4b6092f ("net: convert sock.sk_wmem_alloc from atomic_t to
>>>>> refcount_t") correct? That looks like a statistics counter, not a
>>>>> refcounter? I can't quite tell, though...
>>>>
>>>>
>>>>
>>>> Hmm, yes, it looks a bit weird, but it is used in a refcount fashion
>>>> here:
>>>>
>>>> void sk_free(struct sock *sk)
>>>> {
>>>>         /*
>>>>          * We subtract one from sk_wmem_alloc and can know if
>>>>          * some packets are still in some tx queue.
>>>>          * If not null, sock_wfree() will call __sk_free(sk) later
>>>>          */
>>>>         if (refcount_dec_and_test(&sk->sk_wmem_alloc))
>>>>                 __sk_free(sk);
>>>> }
>>>>
>>>> http://elixir.free-electrons.com/linux/v4.13-rc1/source/net/core/sock.c#L1605
>>>
>>>
>>> Ah yeah, there it is. Hrmpf. Something is triggering WARNs, though...
>>> I wonder if this can get examined more closely?
>>
>>
>> I tried reproducing the error but I don't seem to know how to use lkp. Got
>> lots of permission denied errors and finally ran out of disk space (after
>> using up ~50GB).
>>
>> Maybe I did something wrong?
>>
>> What I did was: Cloned the related kernel repository, checked out offending
>> commit, plopped in config, compiled bzImage. Then I just cloned the lkp repo
>> and tried running the provided command line with the bzImage and provided
>> script.
>>
>> I'll take another look once I have the time, might be I missed something
>> earlier.
>
>Yeah, I'm not sure. Seems it was found through trinity? And only after
>36 seconds, too.

I think I might have missed something here? I cannot find anything about 
trinity or 36 seconds? Although I either misplaced or didn't get the original 
email, so I'm not sure if it had some other attachments beyond the config and 
script?

>
>>> Also, why not atomic->refcount for sk_rmem_alloc?
>>
>> I couldn't find any similar refcount-like use on sk_rmem_alloc.
>
>Okay, interesting.
>
>> And as noted the sk_wmem_alloc thing is also a bit dubious. It looks like it
>> serves a dual purpose of actual allocation size and occasional reference
>> counter.
>
>Could you ask net-dev to see what is actually happening here? This
>looks like a regression, but also very odd (broken?) refcounting ...

Sure, but I'm unsure of what exactly I should be asking? If you have any more 
information on the trinity results I'd be happy to look at that beforehand?

Thanks,
-hans

>
>-Kees
>
>
>-- 
>Kees Cook
>Pixel Security