This is a note to let you know that I've just added the patch titled khugepaged: khugepaged_test_exit() check mmget_still_valid() to the 5.8-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: khugepaged-khugepaged_test_exit-check-mmget_still_valid.patch and it can be found in the queue-5.8 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From bbe98f9cadff58cdd6a4acaeba0efa8565dabe65 Mon Sep 17 00:00:00 2001 From: Hugh Dickins <hughd@xxxxxxxxxx> Date: Thu, 6 Aug 2020 23:26:25 -0700 Subject: khugepaged: khugepaged_test_exit() check mmget_still_valid() From: Hugh Dickins <hughd@xxxxxxxxxx> 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@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx> Cc: Song Liu <songliubraving@xxxxxx> Cc: Mike Kravetz <mike.kravetz@xxxxxxxxxx> Cc: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> [4.8+] Link: http://lkml.kernel.org/r/alpine.LSU.2.11.2008021217020.27773@eggly.anvils Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- 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; Patches currently in stable-queue which might be from hughd@xxxxxxxxxx are queue-5.8/khugepaged-collapse_pte_mapped_thp-flush-the-right-range.patch queue-5.8/hugetlbfs-remove-call-to-huge_pte_alloc-without-i_mmap_rwsem.patch queue-5.8/khugepaged-khugepaged_test_exit-check-mmget_still_valid.patch queue-5.8/khugepaged-retract_page_tables-remember-to-test-exit.patch queue-5.8/khugepaged-collapse_pte_mapped_thp-protect-the-pmd-lock.patch