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

[gang.yan@linux.dev]

July 24, 2026 at 5:48 PM, "Matthieu Baerts" <matttbe@kernel.org mailto:matttbe@kernel.org?to=%22Matthieu%20Baerts%22%20%3Cmatttbe%40kernel.org%3E > wrote:


> 
> 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.
> 

Thank you for your kind reminder. :) 

Cherrs
Gang

> > 
> > Fixes: 8117dac3e7c3 ("selftests: mptcp: add invert check in check_transfer")
> > 
> Thanks!
> 
> Cheers,
> Matt
> -- 
> Sponsored by the NGI0 Core fund.
>