linux-kernel - Re: [PATCH net v2] vsock/test: Fix occasional failure in SIOCOUTQ tests

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Message-ID: <689ab62a-7800-497d-a9a6-3a81e256f98d@linux.ibm.com>
Date: Wed, 7 May 2025 11:01:34 -0500
From: Konstantin Shkolnyy <kshk@...ux.ibm.com>
To: Stefano Garzarella <sgarzare@...hat.com>
Cc: virtualization@...ts.linux.dev, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, mjrosato@...ux.ibm.com
Subject: Re: [PATCH net v2] vsock/test: Fix occasional failure in SIOCOUTQ
 tests

On 07-May-25 10:41, Stefano Garzarella wrote:
> On Wed, 7 May 2025 at 17:15, Konstantin Shkolnyy <kshk@...ux.ibm.com> wrote:
>>
>> These tests:
>>      "SOCK_STREAM ioctl(SIOCOUTQ) 0 unsent bytes"
>>      "SOCK_SEQPACKET ioctl(SIOCOUTQ) 0 unsent bytes"
>> output: "Unexpected 'SIOCOUTQ' value, expected 0, got 64 (CLIENT)".
>>
>> They test that the SIOCOUTQ ioctl reports 0 unsent bytes after the data
>> have been received by the other side. However, sometimes there is a delay
>> in updating this "unsent bytes" counter, and the test fails even though
>> the counter properly goes to 0 several milliseconds later.
>>
>> The delay occurs in the kernel because the used buffer notification
>> callback virtio_vsock_tx_done(), called upon receipt of the data by the
>> other side, doesn't update the counter itself. It delegates that to
>> a kernel thread (via vsock->tx_work). Sometimes that thread is delayed
>> more than the test expects.
>>
>> Change the test to poll SIOCOUTQ until it returns 0 or a timeout occurs.
>>
>> Signed-off-by: Konstantin Shkolnyy <kshk@...ux.ibm.com>
>> ---
>> Changes in v2:
>>   - Use timeout_check() to end polling, instead of counting iterations.
> 
> Why removing the sleep?

I just imagined that whoever uses SIOCOUTQ might want to repeat it 
without a delay, so why not do it, it's a test. Is there a reason to 
insert a sleep?