netdev - Re: reproducable panic eviction work queue

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Date:	Sat, 18 Jul 2015 10:56:35 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Johan Schuijt <johan@...nsip.nl>
Cc:	"nikolay@...hat.com" <nikolay@...hat.com>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"fw@...len.de" <fw@...len.de>,
	"chutzpah@...too.org" <chutzpah@...too.org>,
	Robin Geuze <robing@...nsip.nl>,
	Frank Schreuder <fschreuder@...nsip.nl>,
	netdev <netdev@...r.kernel.org>
Subject: Re: reproducable panic eviction work queue

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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