Commit efdb6720 authored by Hugh Dickins's avatar Hugh Dickins Committed by Linus Torvalds
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mm/rmap: fix munlocking Anon THP with mlocked ptes 

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: d9770fcc ("mm/rmap: fix old bug: munlocking THP missed other mlocks")
Reported-by: default avatarKirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: default avatarHugh Dickins <hughd@google.com>
Acked-by: default avatarKirill 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: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent e73f0f0e

mm/rmap.c

+22 −17
Original line number Diff line number Diff line
@@ -1440,22 +1440,21 @@ 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))) {

		if (!(flags & TTU_IGNORE_MLOCK) &&

		    (vma->vm_flags & VM_LOCKED)) {

			/*

					 * Holding pte lock, we do *not* need

					 * mmap_lock here

			 * 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);

				}

				ret = false;

			page_vma_mapped_walk_done(&pvmw);

			ret = false;

			break;

		}

		}



		/* Unexpected PMD-mapped THP? */

		VM_BUG_ON_PAGE(!pvmw.pte, page);
@@ -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);

}