Re: [RFC PATCH v3 1/8] Use refcount_t for ucounts reference counting

[Alexey Gladkov]

On Mon, Jan 18, 2021 at 11:14:48AM -0800, Linus Torvalds wrote:
> On Fri, Jan 15, 2021 at 6:59 AM Alexey Gladkov <gladkov.alexey@xxxxxxxxx> wrote:
> >
> > @@ -152,10 +153,7 @@ static struct ucounts *get_ucounts(struct user_namespace *ns, kuid_t uid)
> >                         ucounts = new;
> >                 }
> >         }
> > -       if (ucounts->count == INT_MAX)
> > -               ucounts = NULL;
> > -       else
> > -               ucounts->count += 1;
> > +       refcount_inc(&ucounts->count);
> >         spin_unlock_irq(&ucounts_lock);
> >         return ucounts;
> >  }
> 
> This is wrong.
> 
> It used to return NULL when the count saturated.
> 
> Now it just silently saturates.
> 
> I'm not sure how many people care, but that NULL return ends up being
> returned quite widely (through "inc_uncount()" and friends).
> 
> The fact that this has no commit message at all to explain what it is
> doing and why is also a grounds for just NAK.

Sorry about that. I thought that this code is not needed when switching
from int to refcount_t. I was wrong. I'll think about how best to check
it.

-- 
Rgrds, legion