Re: [PATCH v2 1/3] xen/privcmd: Corrected error handling path

[Jürgen Groß <jgross@xxxxxxxx>]

On 07.07.20 13:40, Souptick Joarder wrote:
> On Tue, Jul 7, 2020 at 3:05 PM Jürgen Groß <jgross@xxxxxxxx> wrote:
> > On 06.07.20 20:16, Souptick Joarder wrote:
> > > Previously, if lock_pages() end up partially mapping pages, it used
> > > to return -ERRNO due to which unlock_pages() have to go through
> > > each pages[i] till *nr_pages* to validate them. This can be avoided
> > > by passing correct number of partially mapped pages & -ERRNO separately,
> > > while returning from lock_pages() due to error.
> > >
> > > With this fix unlock_pages() doesn't need to validate pages[i] till
> > > *nr_pages* for error scenario and few condition checks can be ignored.
> > >
> > > Signed-off-by: Souptick Joarder <jrdr.linux@xxxxxxxxx>
> > > Cc: John Hubbard <jhubbard@xxxxxxxxxx>
> > > Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
> > > Cc: Paul Durrant <xadimgnik@xxxxxxxxx>
> > > ---
> > >    drivers/xen/privcmd.c | 31 +++++++++++++++----------------
> > >    1 file changed, 15 insertions(+), 16 deletions(-)
> > >
> > > diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
> > > index a250d11..33677ea 100644
> > > --- a/drivers/xen/privcmd.c
> > > +++ b/drivers/xen/privcmd.c
> > > @@ -580,13 +580,13 @@ static long privcmd_ioctl_mmap_batch(
> > >
> > >    static int lock_pages(
> > >        struct privcmd_dm_op_buf kbufs[], unsigned int num,
> > > -     struct page *pages[], unsigned int nr_pages)
> > > +     struct page *pages[], unsigned int nr_pages, unsigned int *pinned)
> > >    {
> > >        unsigned int i;
> > > +     int page_count = 0;
> > Initial value shouldn't be needed, and ...
> >
> > >        for (i = 0; i < num; i++) {
> > >                unsigned int requested;
> > > -             int pinned;
> > ... you could move the declaration here.
> >
> > With that done you can add my
> >
> > Reviewed-by: Juergen Gross <jgross@xxxxxxxx>
> Ok. But does it going make any difference other than limiting scope ?
Dropping the initializer surely does, and in the end page_count just
replaces the former pinned variable, so why would we want to widen the
scope with this patch?


Juergen