On Wed, 19 Aug 2020, gregkh@xxxxxxxxxxxxxxxxxxx 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;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. 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@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 >
