On Wed, 19 Aug 2020, gregkh@linuxfoundation.org wrote:
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%3Ba=su...
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@vger.kernel.org know about it.
Please hold this one back for the moment: we shall want it, but syzbot detected one place where it can lead to a VM_BUG_ON_MM(). The fix to that is currently in Andrew's tree, but not yet in Linus's - when it gets there, I'll send you its git commit id in reply to this mail.
This patch failed to apply to earlier releases: I'll send the fixup for those at that time. (Fixups for another patch to follow later today.)
Thanks, Hugh
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;Patches currently in stable-queue which might be from hughd@google.com 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