On Wed, 2015-05-27 at 10:56 -0700, Mike Kravetz wrote:
> alloc_huge_page and hugetlb_reserve_pages use region_chg to
> calculate the number of pages which will be added to the reserve
> map. Subpool and global reserve counts are adjusted based on
> the output of region_chg. Before the pages are actually added
> to the reserve map, these routines could race and add fewer
> pages than expected. If this happens, the subpool and global
> reserve counts are not correct.
>
> Compare the number of pages actually added (region_add) to those
> expected to added (region_chg). If fewer pages are actually added,
> this indicates a race and adjust counters accordingly.
>
> Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Reviewed-by: Davidlohr Bueso <dave@xxxxxxxxxxxx>
With one nit below.
> ---
> mm/hugetlb.c | 34 ++++++++++++++++++++++++++++++----
> 1 file changed, 30 insertions(+), 4 deletions(-)
>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index b3d3d59..038c84e 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1544,7 +1544,7 @@ static struct page *alloc_huge_page(struct vm_area_struct *vma,
> struct hugepage_subpool *spool = subpool_vma(vma);
> struct hstate *h = hstate_vma(vma);
> struct page *page;
> - long chg;
> + long chg, commit;
> int ret, idx;
> struct hugetlb_cgroup *h_cg;
>
> @@ -1585,7 +1585,20 @@ static struct page *alloc_huge_page(struct vm_area_struct *vma,
>
> set_page_private(page, (unsigned long)spool);
>
> - vma_commit_reservation(h, vma, addr);
> + commit = vma_commit_reservation(h, vma, addr);
> + if (unlikely(chg > commit)) {
> + /*
> + * The page was added to the reservation map between
> + * vma_needs_reservation and vma_commit_reservation.
> + * This indicates a race with hugetlb_reserve_pages.
> + * Adjust for the subpool count incremented above AND
> + * in hugetlb_reserve_pages for the same page. Also,
> + * the reservation count added in hugetlb_reserve_pages
> + * no longer applies.
> + */
> + hugepage_subpool_put_pages(spool, 1);
> + hugetlb_acct_memory(h, -1);
Should these fixups be encapsulated in a helper? The comment is the same
for both alloc_huge_page and hugetlb_reserve_pages.
Thanks,
Davidlohr
> + }
> return page;
>
> out_uncharge_cgroup:
> @@ -3699,8 +3712,21 @@ int hugetlb_reserve_pages(struct inode *inode,
> * consumed reservations are stored in the map. Hence, nothing
> * else has to be done for private mappings here
> */
> - if (!vma || vma->vm_flags & VM_MAYSHARE)
> - region_add(resv_map, from, to);
> + if (!vma || vma->vm_flags & VM_MAYSHARE) {
> + long add = region_add(resv_map, from, to);
> +
> + if (unlikely(chg > add)) {
> + /*
> + * pages in this range were added to the reserve
> + * map between region_chg and region_add. This
> + * indicates a race with alloc_huge_page. Adjust
> + * the subpool and reserve counts modified above
> + * based on the difference.
> + */
> + hugepage_subpool_put_pages(spool, chg - add);
> + hugetlb_acct_memory(h, -(chg - ret));
> + }
> + }
> return 0;
> out_err:
> if (vma && is_vma_resv_set(vma, HPAGE_RESV_OWNER))
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