Subject: Re: reproducable panic eviction work queue

From: Nikolay Aleksandrov <[email-masked]>
Date: Sat, 18 Jul 2015 12:02:37 +0200

On 07/18/2015 11:01 AM, Johan Schuijt wrote:
> Yes, we already found these and are included in our kernel, but even with these patches we still receive the panic.
> 
> - Johan
> 
> 
>> On 18 Jul 2015, at 10:56, Eric Dumazet <[email-masked]> wrote:
>>
>> On Fri, 2015-07-17 at 21:18 +0000, Johan Schuijt wrote:
>>> Hey guys, 
>>>
>>>
>>> We’re currently running into a reproducible panic in the eviction work
>>> queue code when we pin al our eth* IRQ to different CPU cores (in
>>> order to scale our networking performance for our virtual servers).
>>> This only occurs in kernels >= 3.17 and is a result of the following
>>> change:
>>> https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/commit/?h=linux-3.18.y&id=b13d3cbfb8e8a8f53930af67d1ebf05149f32c24
>>>
>>>
>>> The race/panic we see seems to be the same as, or similar to:
>>> https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/commit/?h=linux-3.18.y&id=65ba1f1ec0eff1c25933468e1d238201c0c2cb29
>>>
>>>
>>> We can confirm that this is directly exposed by the IRQ pinning since
>>> disabling this stops us from being able to reproduce this case :)
>>>
>>>
>>> How te reproduce: in our test-setup we have 4 machines generating UDP
>>> packets which are send to the vulnerable host. These all have a MTU of
>>> 100 (for test purposes) and send UDP packets of a size of 256 bytes.
>>> Within half an hour you will see the following panic:
>>>
>>>
>>> crash> bt
>>> PID: 56     TASK: ffff885f3d9fc210  CPU: 9   COMMAND: "kworker/9:0"
>>> #0 [ffff885f3da03b60] machine_kexec at ffffffff8104a1f7
>>> #1 [ffff885f3da03bb0] crash_kexec at ffffffff810db187
>>> #2 [ffff885f3da03c80] oops_end at ffffffff81015140
>>> #3 [ffff885f3da03ca0] general_protection at ffffffff814f6c88
>>>    [exception RIP: inet_evict_bucket+281]
>>>    RIP: ffffffff81480699  RSP: ffff885f3da03d58  RFLAGS: 00010292
>>>    RAX: ffff885f3da03d08  RBX: dead0000001000a8  RCX:
>>> ffff885f3da03d08
>>>    RDX: 0000000000000006  RSI: ffff885f3da03ce8  RDI:
>>> dead0000001000a8
>>>    RBP: 0000000000000002   R8: 0000000000000286   R9:
>>> ffff88302f401640
>>>    R10: 0000000080000000  R11: ffff88602ec0c138  R12:
>>> ffffffff81a8d8c0
>>>    R13: ffff885f3da03d70  R14: 0000000000000000  R15:
>>> ffff881d6efe1a00
>>>    ORIG_RAX: ffffffffffffffff  CS: 0010  SS: 0018
>>> #4 [ffff885f3da03db0] inet_frag_worker at ffffffff8148075a
>>> #5 [ffff885f3da03e10] process_one_work at ffffffff8107be19
>>> #6 [ffff885f3da03e60] worker_thread at ffffffff8107c6e3
>>> #7 [ffff885f3da03ed0] kthread at ffffffff8108103e
>>> #8 [ffff885f3da03f50] ret_from_fork at ffffffff814f4d7c
>>>
>>>
>>> We would love to receive your input on this matter.
>>>
>>>
>>> Thx in advance,
>>>
>>>
>>> - Johan
>>
>> Check commits 65ba1f1ec0eff1c25933468e1d238201c0c2cb29 &
>> d70127e8a942364de8dd140fe73893efda363293
>>
>> Also please send your mails in text format, not html, and CC netdev ( I
>> did here)
>>
>>>
>>>
>>
>>
> 
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> 

Thank you for the report, I will try to reproduce this locally
Could you please post the full crash log ? Also could you test
with a clean current kernel from Linus' tree or Dave's -net ?
These are available at:
git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
git://git.kernel.org/pub/scm/linux/kernel/git/davem/net
respectively.

One last question how many IRQs do you pin i.e. how many cores
do you actively use for receive ?