[PATCH 1/1] userfaultfd: remove WRITE_ONCE when setting folio->index during UFFDIO_MOVE

Suren Baghdasaryan
2024-04-15T02:08:28Z

When folio is moved with UFFDIO_MOVE it gets locked before the rmap and
index are modified. Due to the folio lock being already held, WRITE_ONCE()
is not needed when setting the folio index. Remove it.

Reported-by: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Lokesh Gidra <lokeshgidra@google.com>
---
mm/huge_memory.c | 2 +-
mm/userfaultfd.c | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 58f2c4745d80..ee12726291f1 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2200,7 +2200,7 @@ int move_pages_huge_pmd(struct mm_struct *mm, pmd_t *dst_pmd, pmd_t *src_pmd, pm
}

folio_move_anon_rmap(src_folio, dst_vma);
- WRITE_ONCE(src_folio->index, linear_page_index(dst_vma, dst_addr));
+ src_folio->index = linear_page_index(dst_vma, dst_addr);

_dst_pmd = mk_huge_pmd(&src_folio->page, dst_vma->vm_page_prot);
/* Follow mremap() behavior and treat the entry dirty after the move */
diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index b70618e8dcd2..575ccf90325a 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -1026,7 +1026,7 @@ static int move_present_pte(struct mm_struct *mm,
}

folio_move_anon_rmap(src_folio, dst_vma);
- WRITE_ONCE(src_folio->index, linear_page_index(dst_vma, dst_addr));
+ src_folio->index = linear_page_index(dst_vma, dst_addr);

orig_dst_pte = mk_pte(&src_folio->page, dst_vma->vm_page_prot);
/* Follow mremap() behavior and treat the entry dirty after the move */

base-commit: 3aec6b2b34e219898883d1e9ea7e911b4d3762a9
--
2.44.0.683.g7961c838ac-goog