linux-kernel - [PATCH v3 4/4] mm: Fix failure to unmap pte on highmem systems

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Date:   Fri,  2 Jun 2023 10:29:49 +0100
From:   Ryan Roberts <ryan.roberts@....com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        SeongJae Park <sj@...nel.org>,
        Christoph Hellwig <hch@...radead.org>
Cc:     Ryan Roberts <ryan.roberts@....com>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Lorenzo Stoakes <lstoakes@...il.com>,
        Uladzislau Rezki <urezki@...il.com>, Zi Yan <ziy@...dia.com>,
        Yu Zhao <yuzhao@...gle.com>, Mike Rapoport <rppt@...nel.org>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        damon@...ts.linux.dev
Subject: [PATCH v3 4/4] mm: Fix failure to unmap pte on highmem systems

The loser of a race to service a pte for a device private entry in the
swap path previously unlocked the ptl, but failed to unmap the pte. This
only affects highmem systems since unmapping a pte is a noop on
non-highmem systems.

Fixes: 16ce101db85d ("mm/memory.c: fix race when faulting a device private page")
Signed-off-by: Ryan Roberts <ryan.roberts@....com>
Reviewed-by: Zi Yan <ziy@...dia.com>
Reviewed-by: Mike Rapoport (IBM) <rppt@...nel.org>
---
 mm/memory.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/mm/memory.c b/mm/memory.c
index f69fbc251198..ed429e20a1bb 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3728,10 +3728,8 @@ vm_fault_t do_swap_page(struct vm_fault *vmf)
 			vmf->page = pfn_swap_entry_to_page(entry);
 			vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd,
 					vmf->address, &vmf->ptl);
-			if (unlikely(!pte_same(*vmf->pte, vmf->orig_pte))) {
-				spin_unlock(vmf->ptl);
-				goto out;
-			}
+			if (unlikely(!pte_same(*vmf->pte, vmf->orig_pte)))
+				goto unlock;
 
 			/*
 			 * Get a page reference while we know the page can't be
-- 
2.25.1