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mm: add !pte_present() check on existing hugetlb_entry callbacks

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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 protected]>
Signed-off-by: Naoya Horiguchi <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: <[email protected]> [3.12+]
Signed-off-by: Andrew Morton <[email protected]>
[ Backported to 3.15.  Signed-off-by: Josh Boyer <[email protected]> ]
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Naoya Horiguchi 2014-06-06 10:00:01 -04:00 • committed by Linus Torvalds
commit d4c54919ed
2 changed files with 6 additions and 2 deletions
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2
fs/proc/task_mmu.c
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@ -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);