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

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

[Suren Baghdasaryan]

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

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

[David Hildenbrand]

On 15.04.24 04:08, Suren Baghdasaryan wrote:
> 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

Reviewed-by: David Hildenbrand <david@redhat.com>

-- 
Cheers,

David / dhildenb

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

[Peter Xu]

On Sun, Apr 14, 2024 at 07:08:21PM -0700, Suren Baghdasaryan wrote:
> 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>

Reviewed-by: Peter Xu <peterx@redhat.com>

-- 
Peter Xu