On Thu, Aug 21, 2014 at 04:43:27PM +0100, Steve Capper wrote:
> +int get_user_pages_fast(unsigned long start, int nr_pages, int write,
> + struct page **pages)
> +{
> + struct mm_struct *mm = current->mm;
> + int nr, ret;
> +
> + start &= PAGE_MASK;
> + nr = __get_user_pages_fast(start, nr_pages, write, pages);
> + ret = nr;
> +
> + if (nr < nr_pages) {
> + /* Try to get the remaining pages with get_user_pages */
> + start += nr << PAGE_SHIFT;
> + pages += nr;
When I read this, my first reaction was... what if nr is negative? In
that case, if nr_pages is positive, we fall through into this if, and
start to wind things backwards - which isn't what we want.
It looks like that can't happen... right? __get_user_pages_fast() only
returns greater-or-equal to zero right now, but what about the future?
> +
> + down_read(&mm->mmap_sem);
> + ret = get_user_pages(current, mm, start,
> + nr_pages - nr, write, 0, pages, NULL);
> + up_read(&mm->mmap_sem);
> +
> + /* Have to be a bit careful with return values */
> + if (nr > 0) {
This kind'a makes it look like nr could be negative.
Other than that, I don't see anything obviously wrong with it.
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