Re: [PATCH] mm: Unsigned 'nr_pages' always larger than zero

[Matthew Wilcox]

On Wed, Sep 04, 2019 at 06:25:19PM +0000, Weiny, Ira wrote:
> > On 9/4/19 12:26 PM, zhong jiang wrote:
> > > With the help of unsigned_lesser_than_zero.cocci. Unsigned 'nr_pages"'
> > > compare with zero. And __get_user_pages_locked will return an long
> > value.
> > > Hence, Convert the long to compare with zero is feasible.
> > 
> > It would be nicer if the parameter nr_pages was long again instead of
> > unsigned long (note there are two variants of the function, so both should be
> > changed).
> 
> Why?  What does it mean for nr_pages to be negative?  The check below seems valid.  Unsigned can be 0 so the check can fail.  IOW Checking unsigned > 0 seems ok.
> 
> What am I missing?

__get_user_pages can return a negative errno.