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Date: Sun, 2 Aug 2020 12:18:35 -0700 (PDT) From: Hugh Dickins <hughd@...gle.com> To: Andrew Morton <akpm@...ux-foundation.org> cc: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>, Andrea Arcangeli <aarcange@...hat.com>, Song Liu <songliubraving@...com>, linux-kernel@...r.kernel.org, linux-mm@...ck.org Subject: [PATCH] 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: 59ea6d06cfa9 ("coredump: fix race condition between collapse_huge_page() and core dumping") Signed-off-by: Hugh Dickins <hughd@...gle.com> Cc: stable@...r.kernel.org # v4.8+ --- Note on stable backporting: the coredump fix was backported as far as v3.16, but this extension only needed where shmem or file THP supported. mm/khugepaged.c | 5 +---- 1 file changed, 1 insertion(+), 4 deletions(-) --- 5.8-rc7/mm/khugepaged.c 2020-07-26 16:58:02.189038680 -0700 +++ linux/mm/khugepaged.c 2020-08-02 10:56:11.105617241 -0700 @@ -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;
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