From mboxrd@z Thu Jan  1 00:00:00 1970
From: Sasha Levin <sasha.levin@oracle.com>
Subject: Re: Network hangs when communicating with host
Date: Fri, 16 Oct 2015 13:25:56 -0400
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References: <CACT4Y+b3kHo0f5VEEZdvRVNL_G0R3yXkXxF7uwCdc_VS7jbhMw@mail.gmail.com>
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Cc: kvm@vger.kernel.org, Kostya Serebryany <kcc@google.com>,
	Evgenii Stepanov <eugenis@google.com>,
	Alexey Samsonov <samsonov@google.com>,
	Alexander Potapenko <glider@google.com>,
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To: Dmitry Vyukov <dvyukov@google.com>, levinsasha928@gmail.com,
	Pekka Enberg <penberg@kernel.org>, asias.hejun@gmail.com,
	penberg@cs.helsinki.fi, gorcunov@gmail.com,
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	matt@ozlabs.org, michael@ellerman.id.au, prasadjoshi124@gmail.com,
	marc.zyngier@arm.com,
	"Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>,
	mingo@elte.hu, gorcunov@openvz.org
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On 10/15/2015 04:20 PM, Dmitry Vyukov wrote:
> Hello,
> 
> I am trying to run a program in lkvm sandbox so that it communicates
> with a program on host. I run lkvm as:
> 
> ./lkvm sandbox --disk sandbox-test --mem=2048 --cpus=4 --kernel
> /arch/x86/boot/bzImage --network mode=user -- /my_prog
> 
> /my_prog then connects to a program on host over a tcp socket.
> I see that host receives some data, sends some data back, but then
> my_prog hangs on network read.
> 
> To localize this I wrote 2 programs (attached). ping is run on host
> and pong is run from lkvm sandbox. They successfully establish tcp
> connection, but after some iterations both hang on read.
> 
> Networking code in Go runtime is there for more than 3 years, widely
> used in production and does not have any known bugs. However, it uses
> epoll edge-triggered readiness notifications that known to be tricky.
> Is it possible that lkvm contains some networking bug? Can it be
> related to the data races in lkvm I reported earlier today?
> 
> I am on commit 3695adeb227813d96d9c41850703fb53a23845eb.

Hey Dmitry,

How long does it take to reproduce? I've been running ping/pong as you've
described and it looks like it doesn't get stuck (read/writes keep going
on both sides).

Can you share your guest kernel config maybe?


Thanks,
Sasha