From bd331906c61bd364f56ba9336a7ff85c6858b1da Mon Sep 17 00:00:00 2001 From: Hugh Dickins Date: Thu, 6 Aug 2020 23:26:25 -0700 Subject: [PATCH] khugepaged: khugepaged_test_exit() check mmget_still_valid() [ Upstream commit bbe98f9cadff58cdd6a4acaeba0efa8565dabe65 ] 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 Signed-off-by: Andrew Morton Cc: Andrea Arcangeli Cc: Song Liu Cc: Mike Kravetz Cc: Kirill A. Shutemov Cc: [4.8+] Link: http://lkml.kernel.org/r/alpine.LSU.2.11.2008021217020.27773@eggly.anvils Signed-off-by: Linus Torvalds Signed-off-by: Sasha Levin --- mm/khugepaged.c | 5 +---- 1 file changed, 1 insertion(+), 4 deletions(-) diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 1d6a9b0b6a9fd..dd592ea9a4a06 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -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. */ 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;