Re: [PATCH mptcp-next 1/2] selftests: mptcp: run fail_test in main shell during join test

[Matthieu Baerts <matttbe@kernel.org>]

On 24/07/2026 11:39, gang.yan@linux.dev wrote:
> July 24, 2026 at 5:28 PM, "Matthieu Baerts" <matttbe@kernel.org mailto:matttbe@kernel.org?to=%22Matthieu%20Baerts%22%20%3Cmatttbe%40kernel.org%3E > wrote:
> 
> 
>>
>> Hi Gang,
>>
>> On 24/07/2026 08:52, Gang Yan wrote:
>>
>>>
>>> From: Gang Yan <yangang@kylinos.cn>
>>>  
>>>  check_transfer() compares the input and output files byte-by-byte using
>>>  `cmp -l "$in" "$out" | while read ...`. Because the while-loop body runs
>>>  in a subshell (the script sets neither lastpipe nor pipefail), the
>>>  fail_test call inside it -- which sets the global ret/last_test_failed --
>>>  and the `return 1` both act on the subshell, not on check_transfer().
>>>  check_transfer() thus always falls through to `return 0`, and any data
>>>  corruption affecting only the payload (leaving the subflow/PM counters
>>>  untouched) is silently reported as PASS.
>>>
>> Good catch!
>>
>> This looks like a fix that should be backported. Do you have a Fixes tag
>> to add here?
> 
> Hi Matt,
> 
> Sorry for that, I originally thought only commits touching ./net/mptcp needed
> a Fixes tag. This fix should be:

"Important" selftests fixes don't need to wait by going to the next
version. If they fix something that can help users and/or CI, they are
as essential as fixes in net/mptcp.

We should just avoid fixes that don't affect results, e.g. the second
patch of this series. But that's also valid for fixes in net/mptcp, e.g.
a fix for a condition that can never happen with the current code, but
will be the case with pending new features.

> Fixes: 8117dac3e7c3 ("selftests: mptcp: add invert check in check_transfer")

Thanks!

Cheers,
Matt
-- 
Sponsored by the NGI0 Core fund.