Re: [linux-pm] hiberante hangs TCP Re: [EXAMPLE CODE] Parasite threadinjection and TCP connection hijacking

[MyungJoo Ham]

On Mon, Oct 31, 2011 at 5:16 AM, Tejun Heo <tj@xxxxxxxxxx> wrote:
> (cc'ing Rafael and linux-pm)
>
> On Sat, Oct 29, 2011 at 11:48:21PM -0500, David Fries wrote:
>> I saw the write up on this on lwn.net, pretty creative by the way, and
>> it got me thinking about a different checkpoint/restart problem I've
>> been running into.  Specifically in hibernating to disk.  In the
>> hibernate case active TCP connections hang after resuming, while an
>> idle TCP connection will continue after the system is back up.  My
>> observation is the kernel checkpoints itself to memory, enables
>> devices, writes out that checkpoint image to storage, then powers off.
>> The problem is if TCP packets are received while writing to storage,
>> the kernel will continue to queue and ack those TCP packets, but the
>> running kernel and it's network state is shortly lost.  When the
>> computer resumes, those TCP byte sequences hang the TCP connection for
>> an extended period of time while the resumed computer refuses to
>> acknowledge the data that was received after checkpointing and the now
>> running kernel knew nothing about, and the other computer tries in
>> vain to resend any data that hadn't yet been acknowledged, which is
>> always after the data that was lost, until one of them eventually
>> gives up.
>>
>> I've been wondering if it was safe or possible to leave any network
>> interfaces down after the checkpoint, or what the right solution would
>> be.  I didn't think marking every TCP connection with a ZOMBIE_KERNEL
>> bit just after the kernel checkpoint (for the kernel is walking dead
>> and won't remember anything that happens), and then prevent any TCP
>> acks from being sent for those connections would be the right
>> solution.  I've taken to unplugging the physical lan cable,
>> hibernating to disk, and plugging it back in after the system is down,
>> to avoid the problem.  Any ideas?
>
> Hmmm... sounds like taking down network interfaces before starting
> hibernation sequence should be enough, which shouldn't be too
> difficult to implement from userland.  Rafael, what do you think?
>
> Thanks.

Um... it seems that the "thaw" callbacks of network interfaces or TCP
should do something on this.

Probably, the "thaw" callbacks should make sure that the TCP
connections are closed?



Cheers,
MyungJoo


>
> --
> tejun
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-- 
MyungJoo Ham, Ph.D.
Mobile Software Platform Lab, DMC Business, Samsung Electronics
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