Re: [PATCH] mm/gup: protect unpin_user_pages() against npages==-ERRNO

[Souptick Joarder]

On Thu, Sep 17, 2020 at 1:11 PM Dan Carpenter <dan.carpenter@xxxxxxxxxx> wrote:
>
> On Wed, Sep 16, 2020 at 11:57:06PM -0700, John Hubbard wrote:
> > As suggested by Dan Carpenter, fortify unpin_user_pages() just a bit,
> > against a typical caller mistake: check if the npages arg is really a
> > -ERRNO value, which would blow up the unpinning loop: WARN and return.
> >
> > If this new WARN_ON() fires, then the system *might* be leaking pages
> > (by leaving them pinned), but probably not. More likely, gup/pup
> > returned a hard -ERRNO error to the caller, who erroneously passed it
> > here.
> >
> > Cc: Ira Weiny <ira.weiny@xxxxxxxxx>
> > Cc: Souptick Joarder <jrdr.linux@xxxxxxxxx>
> > Signed-off-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
> > Signed-off-by: John Hubbard <jhubbard@xxxxxxxxxx>
> > ---
> >
> > Hi Dan,
> >
> > Is is OK to use your signed-off-by here? Since you came up with this.
> >
>
> Yeah.  That's fine.

Do we need a similar check inside unpin_user_pages_dirty_lock(),
when make_dirty set to false ?