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

[Michal Hocko <mhocko@suse.com>]

On Fri 06-06-25 11:01:18, David Hildenbrand wrote:
> On 06.06.25 10:31, Michal Hocko wrote:
[...]
> > Turning them into VM_WARN_ON
> > should be reasonably safe as they are not enabled in production
> > environment anyway so we cannot really rely on those. Having them in
> > WARN form would be still useful for debugging and those that really need
> > a crash dump while debugging can achieve the same result.
> 
> One question is if we should be VM_WARN_ON vs. VM_WARN_ON_ONCE ...

*WARN_ONCE ha a very limited use from code paths which are generally
shared by many callers. You just see one and then nothing. Some time ago
we have discussed an option to have _ONCE per call trace but I haven't
see any follow up.

Anyway starting without _ONCE seems like safer option because we are not
losing potentially useful debugging information. Afterall this is
debugging only thing. But no strong position on my side.

> VM_BUG_ON is essentially a "once" thing so far, but then, we don't continue
> ... so probably most should be _ONCE.
> 
> > 
> > So while I agree that many of them could be dropped or made more clear
> > those could be dealt with after a mass move. An advantage of this would
> > be that we can drop VM_BUG_ON* and stop new instances from being added.
> 
> As a first step we could probably just #define them to go to the
> VM_WARN_ON_* variants and see what happens.

You meand VM_BUG_ON expand to VM_WARN_ON by default?

-- 
Michal Hocko
SUSE Labs