Messages in this thread Patch in this message | | | From | Huang Ying <> | Subject | [PATCH] migrate_pages: silence gcc notes for mis-casting | Date | Thu, 2 Mar 2023 09:26:10 +0800 |
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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@intel.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Baolin Wang <baolin.wang@linux.alibaba.com> Cc: Xin Hao <xhao@linux.alibaba.com> Cc: Zi Yan <ziy@nvidia.com> Cc: Yang Shi <shy828301@gmail.com> Cc: Oscar Salvador <osalvador@suse.de> Cc: Matthew Wilcox <willy@infradead.org> Cc: Bharata B Rao <bharata@amd.com> Cc: Alistair Popple <apopple@nvidia.com> --- 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
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