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SubjectRe: [PATCH v3 2/3] mm: hugetlb: introduce PageHugeActive flag
On Tue 31-03-15 08:50:46, Naoya Horiguchi wrote:
> We are not safe from calling isolate_huge_page() on a hugepage concurrently,
> which can make the victim hugepage in invalid state and results in BUG_ON().

It would be better to be specific about which specific BUG_ON this would
be. I guess you meant different BUG_ONs depending on how the race.

> The root problem of this is that we don't have any information on struct page
> (so easily accessible) about hugepages' activeness. Note that hugepages'
> activeness means just being linked to hstate->hugepage_activelist, which is
> not the same as normal pages' activeness represented by PageActive flag.
>
> Normal pages are isolated by isolate_lru_page() which prechecks PageLRU before
> isolation, so let's do similarly for hugetlb with a new PageHugeActive flag.
>
> Set/ClearPageHugeActive should be called within hugetlb_lock. But hugetlb_cow()
> and hugetlb_no_page() don't do this, being justified because in these function
> SetPageHugeActive is called right after the hugepage is allocated and no other
> thread tries to isolate it.
>
> Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>

The patch itself makes sense to me (even after Andrew's suggestions)

Reviewed-by: Michal Hocko <mhocko@suse.cz>

> ---
> ChangeLog v2->v3:
> - Use PagePrivate of the first tail page to show hugepage's activeness instead
> of PageLRU
> - drop ClearPageLRU in dequeue_hwpoisoned_huge_page() (which was wrong)
> - fix return value of isolate_huge_page() (using ret)
> - move __put_compound_page() part to a separate patch
> - drop "Cc: stable" tag because this is not a simple fix
>
> ChangeLog v1->v2:
> - call isolate_huge_page() in soft_offline_huge_page() instead of list_move()
> ---
> mm/hugetlb.c | 41 ++++++++++++++++++++++++++++++++++++++---
> mm/memory-failure.c | 14 ++++++++++++--
> 2 files changed, 50 insertions(+), 5 deletions(-)
>
> diff --git v4.0-rc6.orig/mm/hugetlb.c v4.0-rc6/mm/hugetlb.c
> index c41b2a0ee273..05e0233d30d7 100644
> --- v4.0-rc6.orig/mm/hugetlb.c
> +++ v4.0-rc6/mm/hugetlb.c
> @@ -855,6 +855,31 @@ struct hstate *size_to_hstate(unsigned long size)
> return NULL;
> }
>
> +/*
> + * Page flag to show that the hugepage is "active/in-use" (i.e. being linked to
> + * hstate->hugepage_activelist.)
> + *
> + * This function can be called for tail pages, but never returns true for them.
> + */
> +int PageHugeActive(struct page *page)
> +{
> + VM_BUG_ON_PAGE(!PageHuge(page), page);
> + return PageHead(page) && PagePrivate(&page[1]);
> +}
> +
> +/* never called for tail page */
> +void SetPageHugeActive(struct page *page)
> +{
> + VM_BUG_ON_PAGE(!PageHeadHuge(page), page);
> + SetPagePrivate(&page[1]);
> +}
> +
> +void ClearPageHugeActive(struct page *page)
> +{
> + VM_BUG_ON_PAGE(!PageHeadHuge(page), page);
> + ClearPagePrivate(&page[1]);
> +}
> +
> void free_huge_page(struct page *page)
> {
> /*
> @@ -875,6 +900,7 @@ void free_huge_page(struct page *page)
> ClearPagePrivate(page);
>
> spin_lock(&hugetlb_lock);
> + ClearPageHugeActive(page);
> hugetlb_cgroup_uncharge_page(hstate_index(h),
> pages_per_huge_page(h), page);
> if (restore_reserve)
> @@ -2891,6 +2917,7 @@ static int hugetlb_cow(struct mm_struct *mm, struct vm_area_struct *vma,
> copy_user_huge_page(new_page, old_page, address, vma,
> pages_per_huge_page(h));
> __SetPageUptodate(new_page);
> + SetPageHugeActive(new_page);
>
> mmun_start = address & huge_page_mask(h);
> mmun_end = mmun_start + huge_page_size(h);
> @@ -3003,6 +3030,7 @@ static int hugetlb_no_page(struct mm_struct *mm, struct vm_area_struct *vma,
> }
> clear_huge_page(page, address, pages_per_huge_page(h));
> __SetPageUptodate(page);
> + SetPageHugeActive(page);
>
> if (vma->vm_flags & VM_MAYSHARE) {
> int err;
> @@ -3812,19 +3840,26 @@ int dequeue_hwpoisoned_huge_page(struct page *hpage)
>
> bool isolate_huge_page(struct page *page, struct list_head *list)
> {
> + bool ret = true;
> +
> VM_BUG_ON_PAGE(!PageHead(page), page);
> - if (!get_page_unless_zero(page))
> - return false;
> spin_lock(&hugetlb_lock);
> + if (!PageHugeActive(page) || !get_page_unless_zero(page)) {
> + ret = false;
> + goto unlock;
> + }
> + ClearPageHugeActive(page);
> list_move_tail(&page->lru, list);
> +unlock:
> spin_unlock(&hugetlb_lock);
> - return true;
> + return ret;
> }
>
> void putback_active_hugepage(struct page *page)
> {
> VM_BUG_ON_PAGE(!PageHead(page), page);
> spin_lock(&hugetlb_lock);
> + SetPageHugeActive(page);
> list_move_tail(&page->lru, &(page_hstate(page))->hugepage_activelist);
> spin_unlock(&hugetlb_lock);
> put_page(page);
> diff --git v4.0-rc6.orig/mm/memory-failure.c v4.0-rc6/mm/memory-failure.c
> index d487f8dc6d39..1d86cca8de26 100644
> --- v4.0-rc6.orig/mm/memory-failure.c
> +++ v4.0-rc6/mm/memory-failure.c
> @@ -1540,8 +1540,18 @@ static int soft_offline_huge_page(struct page *page, int flags)
> }
> unlock_page(hpage);
>
> - /* Keep page count to indicate a given hugepage is isolated. */
> - list_move(&hpage->lru, &pagelist);
> + ret = isolate_huge_page(hpage, &pagelist);
> + if (ret) {
> + /*
> + * get_any_page() and isolate_huge_page() takes a refcount each,
> + * so need to drop one here.
> + */
> + put_page(hpage);
> + } else {
> + pr_info("soft offline: %#lx hugepage failed to isolate\n", pfn);
> + return -EBUSY;
> + }
> +
> ret = migrate_pages(&pagelist, new_page, NULL, MPOL_MF_MOVE_ALL,
> MIGRATE_SYNC, MR_MEMORY_FAILURE);
> if (ret) {
> --
> 1.9.3

--
Michal Hocko
SUSE Labs


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