Re: [PATCH v3 5/5] lib/cpumask: reorganize cpumask_local_spread() logic

[Yury Norov <yury.norov@gmail.com>]

On Thu, Dec 08, 2022 at 08:17:22PM +0000, Peter Lafreniere wrote:
> > Now after moving all NUMA logic into sched_numa_find_nth_cpu(),
> > else-branch of cpumask_local_spread() is just a function call, and
> > we can simplify logic by using ternary operator.
> >
> > While here, replace BUG() with WARN().
> Why make this change? It's still as bad to hit the WARN_ON as it was before.

For example, because of this:

  > Greg, please don't do this
  > 
  > > ChangeSet@1.614, 2002-09-05 08:33:20-07:00, greg@kroah.com
  > >   USB: storage driver: replace show_trace() with BUG()
  > 
  > that BUG() thing is _way_ out of line, and has killed a few of my machines
  > several times for no good reason. It actively hurts debuggability, because
  > the machine is totally dead after it, and the whole and ONLY point of
  > BUG() messages is to help debugging and make it clear that we can't handle
  > something.
  > 
  > In this case, we _can_ handle it, and we're much better off with a machine
  > that works and that you can look up the messages with than killing it.
  > 
  > Rule of thumb: BUG() is only good for something that never happens and
  > that we really have no other option for (ie state is so corrupt that
  > continuing is deadly).
  > 
  > 		Linus