Commit bbe98f9c authored by Hugh Dickins's avatar Hugh Dickins Committed by Linus Torvalds
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khugepaged: khugepaged_test_exit() check mmget_still_valid()

Move collapse_huge_page()'s mmget_still_valid() check into
khugepaged_test_exit() itself.  collapse_huge_page() is used for anon THP
only, and earned its mmget_still_valid() check because it inserts a huge
pmd entry in place of the page table's pmd entry; whereas
collapse_file()'s retract_page_tables() or collapse_pte_mapped_thp()
merely clears the page table's pmd entry.  But core dumping without mmap
lock must have been as open to mistaking a racily cleared pmd entry for a
page table at physical page 0, as exit_mmap() was.  And we certainly have
no interest in mapping as a THP once dumping core.

Fixes: 59ea6d06

 ("coredump: fix race condition between collapse_huge_page() and core dumping")
Signed-off-by: default avatarHugh Dickins <>
Signed-off-by: default avatarAndrew Morton <>
Cc: Andrea Arcangeli <>
Cc: Song Liu <>
Cc: Mike Kravetz <>
Cc: Kirill A. Shutemov <>
Cc: <>	[4.8+]

Signed-off-by: default avatarLinus Torvalds <>
parent 18e77600
......@@ -431,7 +431,7 @@ static void insert_to_mm_slots_hash(struct mm_struct *mm,
static inline int khugepaged_test_exit(struct mm_struct *mm)
return atomic_read(&mm->mm_users) == 0;
return atomic_read(&mm->mm_users) == 0 || !mmget_still_valid(mm);
static bool hugepage_vma_check(struct vm_area_struct *vma,
......@@ -1100,9 +1100,6 @@ static void collapse_huge_page(struct mm_struct *mm,
* handled by the anon_vma lock + PG_lock.
if (!mmget_still_valid(mm))
goto out;
result = hugepage_vma_revalidate(mm, address, &vma);
if (result)
goto out;
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