Re: [PATCH] mm: honor FOLL_GET flag in follow_hugetlb_page v2

[KOSAKI Motohiro]

On Tue, May 7, 2013 at 6:58 PM,  <j.glisse@xxxxxxxxx> wrote:
> From: Jerome Glisse <jglisse@xxxxxxxxxx>
>
> Do not increase page count if FOLL_GET is not set. None of the
> current user can trigger the issue because none of the current
> user call __get_user_pages with both the pages array ptr non
> NULL and the FOLL_GET flags non set in other word all caller
> of __get_user_pages that don't set the FOLL_GET flags also call
> with pages == NULL.

Because, __get_user_pages() doesn't allow pages==NULL and FOLL_GET is on.


long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
{
(snip)
    VM_BUG_ON(!!pages != !!(gup_flags & FOLL_GET));
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