+++ /dev/null
-From bbe98f9cadff58cdd6a4acaeba0efa8565dabe65 Mon Sep 17 00:00:00 2001
-From: Hugh Dickins <hughd@google.com>
-Date: Thu, 6 Aug 2020 23:26:25 -0700
-Subject: khugepaged: khugepaged_test_exit() check mmget_still_valid()
-
-From: Hugh Dickins <hughd@google.com>
-
-commit bbe98f9cadff58cdd6a4acaeba0efa8565dabe65 upstream.
-
-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: 59ea6d06cfa9 ("coredump: fix race condition between collapse_huge_page() and core dumping")
-Signed-off-by: Hugh Dickins <hughd@google.com>
-Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
-Cc: Andrea Arcangeli <aarcange@redhat.com>
-Cc: Song Liu <songliubraving@fb.com>
-Cc: Mike Kravetz <mike.kravetz@oracle.com>
-Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
-Cc: <stable@vger.kernel.org> [4.8+]
-Link: http://lkml.kernel.org/r/alpine.LSU.2.11.2008021217020.27773@eggly.anvils
-Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-
----
- mm/khugepaged.c | 5 +----
- 1 file changed, 1 insertion(+), 4 deletions(-)
-
---- a/mm/khugepaged.c
-+++ b/mm/khugepaged.c
-@@ -431,7 +431,7 @@ static void insert_to_mm_slots_hash(stru
-
- 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
- * handled by the anon_vma lock + PG_lock.
- */
- mmap_write_lock(mm);
-- result = SCAN_ANY_PROCESS;
-- if (!mmget_still_valid(mm))
-- goto out;
- result = hugepage_vma_revalidate(mm, address, &vma);
- if (result)
- goto out;