Re: Backporting Selftests to Stable Kernels?

[Brett A C Sheffield <bacs@librecast.net>]

On 2025-08-23 15:51, Greg KH wrote:
> On Sat, Aug 23, 2025 at 03:05:46PM +0200, Brett Sheffield wrote:
> > Dear Stable Maintainers,
> > 
> > When a bugfix is backported to stable kernels, should we be backporting the
> > associated selftest(s)?
> 
> If you want to, sure!
> 
> > eg.
> > 
> > 9e30ecf23b1b ("net: ipv4: fix incorrect MTU in broadcast routes")
> > was backported to stable, but the selftest was not:
> > 5777d1871bf6 ("selftests: net: add test for variable PMTU in broadcast routes")
> > 
> > Does stable policy say whether it should be?
> 
> It's up to the subsystem/maintainer/developer/whomever if they wish to
> do that or not.  Some subsystems want to do this, others don't, others
> don't care.
> 
> > It does not fix a bug, per se, but it does enable those of us running stable
> > kernel tests to more thoroughly test stable RCs.
> 
> Note that you should always be running the latest selftests for older
> kernels, and I think that's what many of the CI systems are already
> doing, so maybe that's why you don't notice stuff like this?
> 
> That's the only "rule" we have, all new selftests need to work properly
> for older kernels.
> 
> > Should mainline authors be encouraged to mark related tests for backporting?
> 
> Again, it's up to them if they want to or not.  I will point out mptcp
> as one subsystem that does mark selftests to backport, and provides
> backports for when they do not apply correctly.
> 
> hope this helps,

Thanks Greg. It does.


Brett