Re: [PATCH v1] mm/gup: remove (VM_)BUG_ONs

[John Hubbard]

...
> > > > David, what do you think?
> > >
> > > Well, in this patch here I deliberately want _ONCE for the unpin sanity
> > > checks. Because if they start happening (IOW, now after 5 years observed
> > > for the first time?) I *absolutely don't* want to get flooded and
> > > *really* figure out what is going on by seeing what else failed.
> > >
> > > And crashing on VM_BUG_ON() and not observing anything else was also not
> > > particularly helpful :)
> > >
> > > Because ... they shouldn't be happening ...
> > >
> > > (well, it goes back to my initial point about requiring individual
> > > decisions etc ...)
> > >
> > > Not sure what's best now in the general case, in the end I don't care
> > > that much.
> > >
> > > Roll a dice? ;)
> >
> > One last data point: I've often logged onto systems that were running
> > long enough that the dmesg had long since rolled over. And this makes
> > the WARN_ON_ONCE() items disappear.
>
> I think what would be *really* helpful would be quick access to the very 
> first warning that triggered. At least that's what I usually dig for ... :)

These two use cases cannot be simultaneously solved, at least not
perfectly. Fortunately, since a VM_BUG_ON() case cannot ever happen,
either choice will work. hahaha :)

thanks,
--
John Hubbard