From: Hugh Dickins <[email protected]>
[ 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 <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Song Liu <[email protected]>
Cc: Mike Kravetz <[email protected]>
Cc: Kirill A. Shutemov <[email protected]>
Cc: <[email protected]> [4.8+]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Linus Torvalds <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>
---
mm/huge_memory.c | 5 +----
1 file changed, 1 insertion(+), 4 deletions(-)
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index c5628ebc0fc29..1c4d7d2f53d22 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2136,7 +2136,7 @@ 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);
}
int __khugepaged_enter(struct mm_struct *mm)
@@ -2587,9 +2587,6 @@ 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;
if (unlikely(khugepaged_test_exit(mm)))
goto out;
--
2.25.1
