This Linux kernel change "mm: add !pte_present() check on existing hugetlb_entry callbacks" is included in the Linux 3.15 release. This change is authored by Naoya Horiguchi <n-horiguchi [at] ah.jp.nec.com> on Fri Jun 6 10:00:01 2014 -0400. The commit for this change in Linux stable tree is d4c5491 (patch).
mm: add !pte_present() check on existing hugetlb_entry callbacks The age table walker doesn't check non-present hugetlb entry in common path, so hugetlb_entry() callbacks must check it. The reason for this behavior is that some callers want to handle it in its own way. [ I think that reason is bogus, btw - it should just do what the regular code does, which is to call the "pte_hole()" function for such hugetlb entries - Linus] However, some callers don't check it now, which causes unpredictable result, for example when we have a race between migrating hugepage and reading /proc/pid/numa_maps. This patch fixes it by adding !pte_present checks on buggy callbacks. This bug exists for years and got visible by introducing hugepage migration. ChangeLog v2: - fix if condition (check !pte_present() instead of pte_present()) Reported-by: Sasha Levin <email@example.com> Signed-off-by: Naoya Horiguchi <firstname.lastname@example.org> Cc: Rik van Riel <email@example.com> Cc: <firstname.lastname@example.org> [3.12+] Signed-off-by: Andrew Morton <email@example.com> [ Backported to 3.15. Signed-off-by: Josh Boyer <firstname.lastname@example.org> ] Signed-off-by: Linus Torvalds <email@example.com>
There are 8 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.
fs/proc/task_mmu.c | 2 +- mm/mempolicy.c | 6 +++++- 2 files changed, 6 insertions(+), 2 deletions(-) diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c index 442177b..c4b2646 100644 --- a/fs/proc/task_mmu.c +++ b/fs/proc/task_mmu.c @@ -1351,7 +1351,7 @@ static int gather_hugetbl_stats(pte_t *pte, unsigned long hmask, struct numa_maps *md; struct page *page; - if (pte_none(*pte)) + if (!pte_present(*pte)) return 0; page = pte_page(*pte); diff --git a/mm/mempolicy.c b/mm/mempolicy.c index 78e1472..30cc47f8 100644 --- a/mm/mempolicy.c +++ b/mm/mempolicy.c @@ -526,9 +526,13 @@ static void queue_pages_hugetlb_pmd_range(struct vm_area_struct *vma, int nid; struct page *page; spinlock_t *ptl; + pte_t entry; ptl = huge_pte_lock(hstate_vma(vma), vma->vm_mm, (pte_t *)pmd); - page = pte_page(huge_ptep_get((pte_t *)pmd)); + entry = huge_ptep_get((pte_t *)pmd); + if (!pte_present(entry)) + goto unlock; + page = pte_page(entry); nid = page_to_nid(page); if (node_isset(nid, *nodes) == !!(flags & MPOL_MF_INVERT)) goto unlock;