linux-kernel - Re: [PATCH v2 1/6] mm/gup: finish consolidating error handling

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Date:   Mon, 12 Nov 2018 08:14:46 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     Keith Busch <keith.busch@...el.com>
Cc:     John Hubbard <john.hubbard@...il.com>,
        Linux MM <linux-mm@...ck.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-rdma <linux-rdma@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        John Hubbard <jhubbard@...dia.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>
Subject: Re: [PATCH v2 1/6] mm/gup: finish consolidating error handling

On Mon, Nov 12, 2018 at 7:45 AM Keith Busch <keith.busch@...el.com> wrote:
>
> On Sat, Nov 10, 2018 at 12:50:36AM -0800, john.hubbard@...il.com wrote:
> > From: John Hubbard <jhubbard@...dia.com>
> >
> > An upcoming patch wants to be able to operate on each page that
> > get_user_pages has retrieved. In order to do that, it's best to
> > have a common exit point from the routine. Most of this has been
> > taken care of by commit df06b37ffe5a4 ("mm/gup: cache dev_pagemap while
> > pinning pages"), but there was one case remaining.
> >
> > Also, there was still an unnecessary shadow declaration (with a
> > different type) of the "ret" variable, which this commit removes.
> >
> > Cc: Keith Busch <keith.busch@...el.com>
> > Cc: Dan Williams <dan.j.williams@...el.com>
> > Cc: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> > Cc: Dave Hansen <dave.hansen@...el.com>
> > Signed-off-by: John Hubbard <jhubbard@...dia.com>
> > ---
> >  mm/gup.c | 3 +--
> >  1 file changed, 1 insertion(+), 2 deletions(-)
> >
> > diff --git a/mm/gup.c b/mm/gup.c
> > index f76e77a2d34b..55a41dee0340 100644
> > --- a/mm/gup.c
> > +++ b/mm/gup.c
> > @@ -696,12 +696,11 @@ static long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
> >               if (!vma || start >= vma->vm_end) {
> >                       vma = find_extend_vma(mm, start);
> >                       if (!vma && in_gate_area(mm, start)) {
> > -                             int ret;
> >                               ret = get_gate_page(mm, start & PAGE_MASK,
> >                                               gup_flags, &vma,
> >                                               pages ? &pages[i] : NULL);
> >                               if (ret)
> > -                                     return i ? : ret;
> > +                                     goto out;
> >                               ctx.page_mask = 0;
> >                               goto next_page;
> >                       }
>
> This also fixes a potentially leaked dev_pagemap reference count if a
> failure occurs when an iteration crosses a vma boundary. I don't think
> it's normal to have different vma's on a users mapped zone device memory,
> but good to fix anyway.

Does not sound abnormal to me, we should promote this as a fix for the
current cycle with an updated changelog.