Re: [PATCH v2 05/26] mm: gup: allow VM_FAULT_RETRY for multiple times

Jerome Glisse
2019-02-21T16:07:11Z

On Tue, Feb 12, 2019 at 10:56:11AM +0800, Peter Xu wrote:
> This is the gup counterpart of the change that allows the VM_FAULT_RETRY
> to happen for more than once.
>
> Signed-off-by: Peter Xu <peterx@redhat.com>

Reviewed-by: Jérôme Glisse <jglisse@redhat.com>

> ---
> mm/gup.c | 17 +++++++++++++----
> 1 file changed, 13 insertions(+), 4 deletions(-)
>
> diff --git a/mm/gup.c b/mm/gup.c
> index fa75a03204c1..ba387aec0d80 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -528,7 +528,10 @@ static int faultin_page(struct task_struct *tsk, struct vm_area_struct *vma,
> if (*flags & FOLL_NOWAIT)
> fault_flags |= FAULT_FLAG_ALLOW_RETRY | FAULT_FLAG_RETRY_NOWAIT;
> if (*flags & FOLL_TRIED) {
> - VM_WARN_ON_ONCE(fault_flags & FAULT_FLAG_ALLOW_RETRY);
> + /*
> + * Note: FAULT_FLAG_ALLOW_RETRY and FAULT_FLAG_TRIED
> + * can co-exist
> + */
> fault_flags |= FAULT_FLAG_TRIED;
> }
>
> @@ -943,17 +946,23 @@ static __always_inline long __get_user_pages_locked(struct task_struct *tsk,
> /* VM_FAULT_RETRY triggered, so seek to the faulting offset */
> pages += ret;
> start += ret << PAGE_SHIFT;
> + lock_dropped = true;
>
> +retry:
> /*
> * Repeat on the address that fired VM_FAULT_RETRY
> - * without FAULT_FLAG_ALLOW_RETRY but with
> + * with both FAULT_FLAG_ALLOW_RETRY and
> * FAULT_FLAG_TRIED.
> */
> *locked = 1;
> - lock_dropped = true;
> down_read(&mm->mmap_sem);
> ret = __get_user_pages(tsk, mm, start, 1, flags | FOLL_TRIED,
> - pages, NULL, NULL);
> + pages, NULL, locked);
> + if (!*locked) {
> + /* Continue to retry until we succeeded */
> + BUG_ON(ret != 0);
> + goto retry;
> + }
> if (ret != 1) {
> BUG_ON(ret > 1);
> if (!pages_done)
> --
> 2.17.1
>