Commit d9770fcc authored by Hugh Dickins's avatar Hugh Dickins Committed by Linus Torvalds
Browse files

mm/rmap: fix old bug: munlocking THP missed other mlocks

The kernel recovers in due course from missing Mlocked pages: but there
was no point in calling page_mlock() (formerly known as
try_to_munlock()) on a THP, because nothing got done even when it was
found to be mapped in another VM_LOCKED vma.

It's true that we need to be careful: Mlocked accounting of pte-mapped
THPs is too difficult (so consistently avoided); but Mlocked accounting
of only-pmd-mapped THPs is supposed to work, even when multiple mappings
are mlocked and munlocked or munmapped.  Refine the tests.

There is already a VM_BUG_ON_PAGE(PageDoubleMap) in page_mlock(), so
page_mlock_one() does not even have to worry about that complication.

(I said the kernel recovers: but would page reclaim be likely to split
THP before rediscovering that it's VM_LOCKED? I've not followed that up)

Fixes: 9a73f61b

 ("thp, mlock: do not mlock PTE-mapped file huge pages")
Signed-off-by: default avatarHugh Dickins <>
Reviewed-by: default avatarShakeel Butt <>
Acked-by: default avatarKirill A. Shutemov <>

Cc: Andrew Morton <>
Cc: Alistair Popple <>
Cc: Jason Gunthorpe <>
Cc: Ralph Campbell <>
Cc: Christoph Hellwig <>
Cc: Yang Shi <>
Signed-off-by: default avatarLinus Torvalds <>
parent 64b586d1
......@@ -1442,8 +1442,9 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
if (!(flags & TTU_IGNORE_MLOCK)) {
if (vma->vm_flags & VM_LOCKED) {
/* PTE-mapped THP are never mlocked */
if (!PageTransCompound(page)) {
/* PTE-mapped THP are never marked as mlocked */
if (!PageTransCompound(page) ||
(PageHead(page) && !PageDoubleMap(page))) {
* Holding pte lock, we do *not* need
* mmap_lock here
......@@ -1984,9 +1985,11 @@ static bool page_mlock_one(struct page *page, struct vm_area_struct *vma,
* munlock_vma_pages_range().
if (vma->vm_flags & VM_LOCKED) {
/* PTE-mapped THP are never mlocked */
if (!PageTransCompound(page))
* PTE-mapped THP are never marked as mlocked, but
* this function is never called when PageDoubleMap().
Markdown is supported
0% or .
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment