The patch below does not apply to the 4.4-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@xxxxxxxxxxxxxxx>.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
>From bbe98f9cadff58cdd6a4acaeba0efa8565dabe65 Mon Sep 17 00:00:00 2001
From: Hugh Dickins <hughd@xxxxxxxxxx>
Date: Thu, 6 Aug 2020 23:26:25 -0700
Subject: [PATCH] khugepaged: khugepaged_test_exit() check mmget_still_valid()
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>
diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index ac04b332a373..b52bd46ad146 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -431,7 +431,7 @@ 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,
@@ -1100,9 +1100,6 @@ static void collapse_huge_page(struct mm_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;
