[PATCH 3.14 68/78] mm: add !pte_present() check on existing hugetlb_entry callbacks

Greg Kroah-Hartman
2014-06-09T22:46:28Z

From: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>

commit d4c54919ed86302094c0ca7d48a8cbd4ee753e92 upstream.

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 <sasha.levin@oracle.com>
Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
[ Backported to 3.15. Signed-off-by: Josh Boyer <jwboyer@fedoraproject.org> ]
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/proc/task_mmu.c | 2 +-
mm/mempolicy.c | 6 +++++-
2 files changed, 6 insertions(+), 2 deletions(-)

--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -1350,7 +1350,7 @@ static int gather_hugetbl_stats(pte_t *p
struct numa_maps *md;
struct page *page;

- if (pte_none(*pte))
+ if (!pte_present(*pte))
return 0;

page = pte_page(*pte);
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -526,9 +526,13 @@ static void queue_pages_hugetlb_pmd_rang
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;