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

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Message-ID: <CAFqt6zYXnD2VvGNcAnLC3BTyA4vSBpFLHQq3h+BzEDQcGRJD2w@mail.gmail.com>
Date:   Wed, 8 Jul 2020 07:37:00 +0530
From:   Souptick Joarder <jrdr.linux@...il.com>
To:     Jürgen Groß <jgross@...e.com>
Cc:     Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        sstabellini@...nel.org, xen-devel@...ts.xenproject.org,
        linux-kernel@...r.kernel.org, John Hubbard <jhubbard@...dia.com>,
        Paul Durrant <xadimgnik@...il.com>
Subject: Re: [PATCH v2 1/3] xen/privcmd: Corrected error handling path

On Tue, Jul 7, 2020 at 5:15 PM Jürgen Groß <jgross@...e.com> wrote:
>
> On 07.07.20 13:40, Souptick Joarder wrote:
> > On Tue, Jul 7, 2020 at 3:05 PM Jürgen Groß <jgross@...e.com> 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@...il.com>
> >>> Cc: John Hubbard <jhubbard@...dia.com>
> >>> Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>
> >>> Cc: Paul Durrant <xadimgnik@...il.com>
> >>> ---
> >>>    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@...e.com>
> >
> > 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?

Agree, no reason to move it up. Will change it in v3.

>
>
> Juergen