linux-kernel - [PATCH 3/4] mm/rmap: fix new bug: premature return from page_mlock

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Date:   Wed, 7 Jul 2021 13:11:24 -0700 (PDT)
From:   Hugh Dickins <hughd@...gle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
cc:     Hugh Dickins <hughd@...gle.com>,
        Alistair Popple <apopple@...dia.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Ralph Campbell <rcampbell@...dia.com>,
        Christoph Hellwig <hch@....de>, Yang Shi <shy828301@...il.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: [PATCH 3/4] mm/rmap: fix new bug: premature return from
 page_mlock_one()

In the unlikely race case that page_mlock_one() finds VM_LOCKED has been
cleared by the time it got page table lock, page_vma_mapped_walk_done()
must be called before returning, either explicitly, or by a final call
to page_vma_mapped_walk() - otherwise the page table remains locked.

Fixes: cd62734ca60d ("mm/rmap: split try_to_munlock from try_to_unmap")
Signed-off-by: Hugh Dickins <hughd@...gle.com>
---
 mm/rmap.c | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/mm/rmap.c b/mm/rmap.c
index 0e83c3be8568..1235368f0628 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1990,14 +1990,13 @@ static bool page_mlock_one(struct page *page, struct vm_area_struct *vma,
 			 * this function is never called when PageDoubleMap().
 			 */
 			mlock_vma_page(page);
+			/*
+			 * No need to scan further once the page is marked
+			 * as mlocked.
+			 */
 			page_vma_mapped_walk_done(&pvmw);
+			return false;
 		}
-
-		/*
-		 * no need to continue scanning other vma's if the page has
-		 * been locked.
-		 */
-		return false;
 	}
 
 	return true;
-- 
2.26.2