Re: [PATCH] kgdb: Avoid suspicious RCU usage warning

From: Daniel Thompson
Date: Wed Jun 03 2020 - 08:00:58 EST

On Tue, Jun 02, 2020 at 03:56:33PM -0700, Doug Anderson wrote:
> > > 2. Perhaps remove the whole irq saving / restoring in kgdb_cpu_enter().
> >
> > Are you feeling lucky?
> >
> > I think there will come a time when bravery is called for but I'd rather
> > see this as part of a bigger rewrite instead of a single high risk
> > change.
> Hrm, maybe. I guess it depends on whether we want to take baby steps
> there or try to do it all at once. If we take baby steps we will
> occasionally fall down but we'll slowly start getting things cleaned
> up. If we wait for a full rewrite then we might be waiting for a long
> time. It'll also be harder to figure out which of the big changes in
> the major rewrite broken someone. ...or if the major rewrite comes in
> 20 small/bisectable patches it may be hard to revert patch 2 out of 20
> if the future patches all build upon it. If we do one small high-risk
> change and then wait before building upon it then it'll be easy for
> someone to bisect and then yell for a revert.

My views are a bit too nuanced for me to agree or disagree with this.
I'm not against baby steps and I definitely *don't* want kgdb to
continue to be preserved in aspic.

However I'm still reluctant to start our baby steps with a "let's see
if this breaks something" patch given we know it could be a very large
number of kernel cycles before we get an answer. I would be much
happier if those baby steps started, for example, with refactoring to
decompose the beast into clearer (and dare I say better documented)

Or put another way, even if someone sent me 20 small bisectable patches
in a single kernel cycle I'd still want the high risk bits to be
towards the end of the patch set.