The following GCC notes was reported for commit 64c8902ed441
("migrate_pages: split unmap_and_move() to _unmap() and _move()").
mm/migrate.c: In function ‘__migrate_folio_extract’:
mm/migrate.c:1050:20: note: randstruct: casting between randomized
structure pointer types (ssa): ‘struct anon_vma’ and ‘struct
address_space’
1050 | *anon_vmap = (void *)dst->mapping;
| ~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~
The casting itself is safe. Because we only use dst->mapping to store
the pointer itself temporarily and dst is a newly allocated folio and
not used by anyone else during that. But the notes should be silenced
and some comments are deserved. So, we do that in this patch.
Fixes: 64c8902ed441 ("migrate_pages: split unmap_and_move() to _unmap() and _move()")
Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
Cc: Xin Hao <xhao@xxxxxxxxxxxxxxxxx>
Cc: Zi Yan <ziy@xxxxxxxxxx>
Cc: Yang Shi <shy828301@xxxxxxxxx>
Cc: Oscar Salvador <osalvador@xxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Bharata B Rao <bharata@xxxxxxx>
Cc: Alistair Popple <apopple@xxxxxxxxxx>
---
mm/migrate.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)
diff --git a/mm/migrate.c b/mm/migrate.c
index c17ce5ee8d92..53fcc23025c7 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1047,7 +1047,16 @@ static void __migrate_folio_extract(struct folio *dst,
int *page_was_mappedp,
struct anon_vma **anon_vmap)
{
- *anon_vmap = (void *)dst->mapping;
+ struct anon_vma *anon_vma;
+
+ /*
+ * 2 steps assignment to silence gcc notes for mis-casting. The
+ * casting is safe. Because we only use dst->mapping to store
+ * the pointer itself temporarily and dst is a newly allocated
+ * folio and not used by anyone else during that.
+ */
+ anon_vma = (void *)dst->mapping;
+ *anon_vmap = anon_vma;
*page_was_mappedp = (unsigned long)dst->private;
dst->mapping = NULL;
dst->private = NULL;
--
2.39.2
