Date:   Tue, 25 Jul 2017 13:43:45 +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 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.

>
>Also, why not atomic->refcount for sk_rmem_alloc?

I couldn't find any similar refcount-like use on sk_rmem_alloc.

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.

Regards,
-hans

>
>-Kees
>
>>
>> And here:
>>
>>         if (refcount_sub_and_test(len, &sk->sk_wmem_alloc))
>>                 __sk_free(sk);
>> }
>> http://elixir.free-electrons.com/linux/v4.13-rc1/source/net/core/sock.c#L1798
>>
>>>
>>> I think this WARN is from:
>>>
>>> WARN_ON(refcount_read(&sk->sk_wmem_alloc));
>>
>>
>> I looked through the commit and couldn't find any direct conversion issues.
>> Although I guess it is debatable whether refcoun_t should be used in this
>> kind of less conventional case.
>>
>> The only potential problem I noticed was that based on the following change
>> (or rather the original code) it seems like sk_wmem_alloc could sometimes be
>> negative. I'm not familiar enough with the code to say whether that really
>> is the case.
>>
>> --- a/drivers/atm/fore200e.c
>> +++ b/drivers/atm/fore200e.c
>> @@ -924,12 +924,7 @@ fore200e_tx_irq(struct fore200e* fore200e)
>>                else {
>>                    dev_kfree_skb_any(entry->skb);
>>                }
>> -#if 1
>> -               /* race fixed by the above incarnation mechanism, but... */
>> -               if (atomic_read(&sk_atm(vcc)->sk_wmem_alloc) < 0) {
>> -                   atomic_set(&sk_atm(vcc)->sk_wmem_alloc, 0);
>> -               }
>> -#endif
>> +
>>                /* check error condition */
>>                if (*entry->status & STATUS_ERROR)
>>                    atomic_inc(&vcc->stats->tx_err);
>>
>> But if this is actually supposed to legitimately happen and eventually
>> "balance out" refcount_t might not work here. On the other hand this should
>> have triggered an earlier WARN_ON already, so it doesn't seem to be the
>> issue here?
>>
>> Regards,
>> -hans
>>
>>
>>>
>>> -Kees
>>>
>>> On Sun, Jul 23, 2017 at 7:13 PM, kernel test robot
>>> <xiaolong.ye@...el.com> wrote:
>>>>
>>>>
>>>> FYI, we noticed the following commit:
>>>>
>>>> commit: b631e535c61d7ddbb7ebac545f729ca9b3b6d70e ("x86/refcount:
>>>> Implement fast refcount overflow protection")
>>>> https://git.kernel.org/cgit/linux/kernel/git/kees/linux.git
>>>> kspp/fast-refcount/ud/v6
>>>>
>>>> in testcase: boot
>>>>
>>>> on test machine: qemu-system-x86_64 -enable-kvm -smp 2 -m 512M
>>>>
>>>> caused below changes (please refer to attached dmesg/kmsg for entire
>>>> log/backtrace):
>>>>
>>>>
>>>>
>>>> +------------------------------------------------------------+------------+------------+
>>>> |                                                            | 561ee9566e
>>>> | b631e535c6 |
>>>>
>>>> +------------------------------------------------------------+------------+------------+
>>>> | boot_successes                                             | 37
>>>> | 0          |
>>>> | boot_failures                                              | 0
>>>> | 4          |
>>>> | WARNING:at_net/netlink/af_netlink.c:#netlink_sock_destruct | 0
>>>> | 4          |
>>>>
>>>> +------------------------------------------------------------+------------+------------+
>>>>
>>>>
>>>>
>>>> [   36.991339] WARNING: CPU: 0 PID: 280 at net/netlink/af_netlink.c:374
>>>> netlink_sock_destruct+0x1ea/0x200
>>>> [   36.994035] Modules linked in:
>>>> [   36.994815] CPU: 0 PID: 280 Comm: sh Not tainted
>>>> 4.13.0-rc1-00003-gb631e53 #1
>>>> [   36.996546] task: ffff88001448c180 task.stack: ffffc900004e0000
>>>> [   36.998006] RIP: 0010:netlink_sock_destruct+0x1ea/0x200
>>>> [   36.999290] RSP: 0018:ffffffff82433de0 EFLAGS: 00010206
>>>> [   37.000591] RAX: ffff88001448c180 RBX: ffff880016a3d000 RCX:
>>>> 0000000000000000
>>>> [   37.002319] RDX: 0000000000000100 RSI: 0000000000000001 RDI:
>>>> ffffffff82796f48
>>>> [   37.004061] RBP: ffffffff82433df0 R08: 0000000000000000 R09:
>>>> 0000000000000000
>>>> [   37.005780] R10: 0000000000000001 R11: 0000000000000001 R12:
>>>> 0000000000000001
>>>> [   37.007528] R13: ffffffff81cd4a00 R14: 96e49674e09954cf R15:
>>>> 000000000000001f
>>>> [   37.009261] FS:  0000000000000000(0000) GS:ffffffff82430000(0000)
>>>> knlGS:0000000000000000
>>>> [   37.011233] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>>>> [   37.012629] CR2: 00007f268a96e688 CR3: 00000000159ff000 CR4:
>>>> 00000000000006b0
>>>> [   37.014212] Call Trace:
>>>> [   37.014745]  <IRQ>
>>>> [   37.015201]  __sk_destruct+0x3a2/0x4c0
>>>> [   37.015994]  sk_destruct+0x3f/0x70
>>>> [   37.016747]  __sk_free+0x10d/0x160
>>>> [   37.017479]  sk_free+0x4a/0x60
>>>> [   37.018127]  deferred_put_nlk_sk+0xd9/0xf0
>>>> [   37.018998]  rcu_process_callbacks+0x766/0x1cb0
>>>> [   37.019944]  ? rcu_process_callbacks+0x643/0x1cb0
>>>> [   37.020960]  __do_softirq+0x10c/0x6b2
>>>> [   37.021749]  irq_exit+0x135/0x140
>>>> [   37.022458]  smp_apic_timer_interrupt+0x3b/0x50
>>>> [   37.023429]  apic_timer_interrupt+0x8e/0xa0
>>>> [   37.024303] RIP: 0010:__sanitizer_cov_trace_pc+0x0/0x60
>>>> [   37.025141] RSP: 0018:ffffc900004e3c10 EFLAGS: 00000246 ORIG_RAX:
>>>> ffffffffffffff10
>>>> [   37.026605] RAX: ffff88001448c180 RBX: ffffffff82727288 RCX:
>>>> 0000000000000000
>>>> [   37.028340] RDX: 0000000000000000 RSI: 0000000000000000 RDI:
>>>> ffffffff82727288
>>>> [   37.030077] RBP: ffffc900004e3c60 R08: 0000000000000000 R09:
>>>> 0000000000000000
>>>> [   37.031796] R10: 0000000000000000 R11: 0000000000000001 R12:
>>>> 0000000000000000
>>>> [   37.033546] R13: 0000000000000000 R14: 0000000000000000 R15:
>>>> 00007f2689f93000
>>>> [   37.035262]  </IRQ>
>>>> [   37.035814]  ? ftrace_likely_update+0x39/0x200
>>>> [   37.036925]  ? vm_normal_page+0xd7/0x1a0
>>>> [   37.037886]  unmap_page_range+0x775/0x14d0
>>>> [   37.038658]  unmap_single_vma+0x158/0x180
>>>> [   37.039403]  unmap_vmas+0x5b/0x80
>>>> [   37.040202]  exit_mmap+0x118/0x220
>>>> [   37.040900]  mmput+0xd5/0x240
>>>> [   37.041479]  do_exit+0xdb6/0x16d0
>>>> [   37.042183]  ? entry_SYSCALL_64_fastpath+0x5/0xbd
>>>> [   37.043365]  do_group_exit+0x8a/0x160
>>>> [   37.044282]  SyS_exit_group+0x1d/0x20
>>>> [   37.045192]  entry_SYSCALL_64_fastpath+0x1f/0xbd
>>>> [   37.046321] RIP: 0033:0x7f268a676408
>>>> [   37.047221] RSP: 002b:00007ffcba052ea8 EFLAGS: 00000246 ORIG_RAX:
>>>> 00000000000000e7
>>>> [   37.049042] RAX: ffffffffffffffda RBX: 000000000000007f RCX:
>>>> 00007f268a676408
>>>> [   37.050784] RDX: 000000000000007f RSI: 000000000000003c RDI:
>>>> 000000000000007f
>>>> [   37.052512] RBP: 00007f268a96e688 R08: 00000000000000e7 R09:
>>>> ffffffffffffffa0
>>>> [   37.054281] R10: 0000000000000000 R11: 0000000000000246 R12:
>>>> 00007f268a96ff40
>>>> [   37.056004] R13: 0000000000000001 R14: 0000000000000000 R15:
>>>> 00000000ffffffff
>>>> [   37.057765] Code: e8 56 14 48 ff eb ca e8 b5 42 4f ff 0f ff 0f 1f 00
>>>> eb a7 e8 a9 42 4f ff 0f ff 0f 1f 80 00 00 00 00 e9 48 ff ff ff e8 96 42 4f
>>>> ff <0f> ff 0f 1f 40 00 e9 e5 fe ff ff 90 66 2e 0f 1f 84 00 00 00 00
>>>> [   37.062621] ---[ end trace db04ba531557bbda ]---
>>>>
>>>>
>>>> To reproduce:
>>>>
>>>>         git clone https://github.com/01org/lkp-tests.git
>>>>         cd lkp-tests
>>>>         bin/lkp qemu -k <bzImage> job-script  # job-script is attached in
>>>> this email
>>>>
>>>>
>>>>
>>>> Thanks,
>>>> Xiaolong
>>>
>>>
>>>
>>>
>>> --
>>> Kees Cook
>>> Pixel Security
>
>
>
>-- 
>Kees Cook
>Pixel Security

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