[PATCH 4.19 03/71] khugepaged: khugepaged_test_exit() check mmget_still_valid()

Greg Kroah-Hartman
2020-08-24T08:56:13Z

From: Hugh Dickins <hughd@google.com>

[ 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@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: Sasha Levin <sashal@kernel.org>
---
mm/khugepaged.c | 5 +----
1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 483c4573695a9..fbb3ac9ce0869 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -394,7 +394,7 @@ 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,
@@ -1005,9 +1005,6 @@ 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;
--
2.25.1