Re: [PATCH v2 1/6] mm: get_user_pages: consolidate error handling

Jan Kara
2018-07-02T10:17:25Z

On Sun 01-07-18 17:56:49, john.hubbard@gmail.com wrote:
> From: John Hubbard <jhubbard@nvidia.com>
>
> An upcoming patch requires a way to operate on each page that
> any of the get_user_pages_*() variants returns.
>
> In preparation for that, consolidate the error handling for
> __get_user_pages(). This provides a single location (the "out:" label)
> for operating on the collected set of pages that are about to be returned.
>
> As long every use of the "ret" variable is being edited, rename
> "ret" --> "err", so that its name matches its true role.
> This also gets rid of two shadowed variable declarations, as a
> tiny beneficial a side effect.
>
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>

This looks nice! You can add:

Reviewed-by: Jan Kara <jack@suse.cz>

Honza

> ---
> mm/gup.c | 37 ++++++++++++++++++++++---------------
> 1 file changed, 22 insertions(+), 15 deletions(-)
>
> diff --git a/mm/gup.c b/mm/gup.c
> index b70d7ba7cc13..73f0b3316fa7 100644
> --- a/mm/gup.c
> +++ b/mm/gup.c
> @@ -660,6 +660,7 @@ static long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
> struct vm_area_struct **vmas, int *nonblocking)
> {
> long i = 0;
> + int err = 0;
> unsigned int page_mask;
> struct vm_area_struct *vma = NULL;
>
> @@ -685,18 +686,19 @@ 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,
> + err = get_gate_page(mm, start & PAGE_MASK,
> gup_flags, &vma,
> pages ? &pages[i] : NULL);
> - if (ret)
> - return i ? : ret;
> + if (err)
> + goto out;
> page_mask = 0;
> goto next_page;
> }
>
> - if (!vma || check_vma_flags(vma, gup_flags))
> - return i ? : -EFAULT;
> + if (!vma || check_vma_flags(vma, gup_flags)) {
> + err = -EFAULT;
> + goto out;
> + }
> if (is_vm_hugetlb_page(vma)) {
> i = follow_hugetlb_page(mm, vma, pages, vmas,
> &start, &nr_pages, i,
> @@ -709,23 +711,25 @@ static long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
> * If we have a pending SIGKILL, don't keep faulting pages and
> * potentially allocating memory.
> */
> - if (unlikely(fatal_signal_pending(current)))
> - return i ? i : -ERESTARTSYS;
> + if (unlikely(fatal_signal_pending(current))) {
> + err = -ERESTARTSYS;
> + goto out;
> + }
> cond_resched();
> page = follow_page_mask(vma, start, foll_flags, &page_mask);
> if (!page) {
> - int ret;
> - ret = faultin_page(tsk, vma, start, &foll_flags,
> + err = faultin_page(tsk, vma, start, &foll_flags,
> nonblocking);
> - switch (ret) {
> + switch (err) {
> case 0:
> goto retry;
> case -EFAULT:
> case -ENOMEM:
> case -EHWPOISON:
> - return i ? i : ret;
> + goto out;
> case -EBUSY:
> - return i;
> + err = 0;
> + goto out;
> case -ENOENT:
> goto next_page;
> }
> @@ -737,7 +741,8 @@ static long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
> */
> goto next_page;
> } else if (IS_ERR(page)) {
> - return i ? i : PTR_ERR(page);
> + err = PTR_ERR(page);
> + goto out;
> }
> if (pages) {
> pages[i] = page;
> @@ -757,7 +762,9 @@ static long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
> start += page_increm * PAGE_SIZE;
> nr_pages -= page_increm;
> } while (nr_pages);
> - return i;
> +
> +out:
> + return i ? i : err;
> }
>
> static bool vma_permits_fault(struct vm_area_struct *vma,
> --
> 2.18.0
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR