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mm/rmap: fix munlocking Anon THP with mlocked ptes

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Many thanks to Kirill for reminding that PageDoubleMap cannot be relied on
to warn of pte mappings in the Anon THP case; and a scan of subpages does
not seem appropriate here.  Note how follow_trans_huge_pmd() does not even
mark an Anon THP as mlocked when compound_mapcount != 1: multiple mlocking
of Anon THP is avoided, so simply return from page_mlock() in this case.

Link: https://lore.kernel.org/lkml/cfa154c-d595-406-eb7d-eb9df730f944@google.com/
Fixes: d9770fcc1c ("mm/rmap: fix old bug: munlocking THP missed other mlocks")
Reported-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Hugh Dickins <hughd@google.com>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Shakeel Butt <shakeelb@google.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Hugh Dickins 2021-07-11 20:10:49 -07:00 committed by Linus Torvalds
parent e73f0f0ee7
commit efdb6720b4
1 changed files with 22 additions and 17 deletions
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39
mm/rmap.c
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@ -1440,21 +1440,20 @@ static bool try_to_unmap_one(struct page *page, struct vm_area_struct *vma,
/*
* If the page is mlock()d, we cannot swap it out.
*/
if (!(flags & TTU_IGNORE_MLOCK)) {
if (vma->vm_flags & VM_LOCKED) {
/* 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
*/
mlock_vma_page(page);
}
ret = false;
page_vma_mapped_walk_done(&pvmw);
break;
}
if (!(flags & TTU_IGNORE_MLOCK) &&
(vma->vm_flags & VM_LOCKED)) {
/*
* PTE-mapped THP are never marked as mlocked: so do
* not set it on a DoubleMap THP, nor on an Anon THP
* (which may still be PTE-mapped after DoubleMap was
* cleared). But stop unmapping even in those cases.
*/
if (!PageTransCompound(page) || (PageHead(page) &&
!PageDoubleMap(page) && !PageAnon(page)))
mlock_vma_page(page);
page_vma_mapped_walk_done(&pvmw);
ret = false;
break;
}
/* Unexpected PMD-mapped THP? */
@ -1986,8 +1985,10 @@ static bool page_mlock_one(struct page *page, struct vm_area_struct *vma,
*/
if (vma->vm_flags & VM_LOCKED) {
/*
* PTE-mapped THP are never marked as mlocked, but
* this function is never called when PageDoubleMap().
* PTE-mapped THP are never marked as mlocked; but
* this function is never called on a DoubleMap THP,
* nor on an Anon THP (which may still be PTE-mapped
* after DoubleMap was cleared).
*/
mlock_vma_page(page);
/*
@ -2022,6 +2023,10 @@ void page_mlock(struct page *page)
VM_BUG_ON_PAGE(!PageLocked(page) || PageLRU(page), page);
VM_BUG_ON_PAGE(PageCompound(page) && PageDoubleMap(page), page);
/* Anon THP are only marked as mlocked when singly mapped */
if (PageTransCompound(page) && PageAnon(page))
return;
rmap_walk(page, &rwc);
}