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 5.7-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_va.patch and it can be found in the queue-5.7 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit 9f869065c86b003ab703840bb8bb6320d780a4ae Author: Hugh Dickins <hughd@xxxxxxxxxx> Date: Thu Aug 6 23:26:25 2020 -0700 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 <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: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/mm/khugepaged.c b/mm/khugepaged.c index 38874fe112d58..9e7cec2840927 100644 --- a/mm/khugepaged.c +++ b/mm/khugepaged.c @@ -400,7 +400,7 @@ 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, @@ -1016,9 +1016,6 @@ static void collapse_huge_page(struct mm_struct *mm, * handled by the anon_vma lock + PG_lock. */ down_write(&mm->mmap_sem); - result = SCAN_ANY_PROCESS; - if (!mmget_still_valid(mm)) - goto out; result = hugepage_vma_revalidate(mm, address, &vma); if (result) goto out;