Messages in this thread Patch in this message | | | Date | Sat, 4 Mar 2023 15:20:58 -0800 | From | Andrew Morton <> | Subject | Re: [GIT PULL] hotfixes for 6.3-rc1 |
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On Sat, 4 Mar 2023 14:35:00 -0800 Linus Torvalds <torvalds@linux-foundation.org> wrote:
> On Sat, Mar 4, 2023 at 1:15 PM Andrew Morton <akpm@linux-foundation.org> wrote: > > > > 17 hotfixes. Eight are for MM and seven are for other parts of the > > kernel. Seven are cc:stable and eight address post-6.3 issues or were > > judged unsuitable for -stable backporting. > > Hmm. Since this pull didn't fix the gcc note about playing pointer > games that I get for my allmodconfig test build, and since I _really_ > don't want to have an rc1 release tomorrow with that (valid) warning, > I fixed it up myself.
Ah. Ying did it this way:
From: Huang Ying <ying.huang@intel.com> Subject: migrate_pages: silence gcc notes for mis-casting Date: Thu, 2 Mar 2023 09:26:10 +0800
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.
Link: https://lkml.kernel.org/r/20230302012610.17055-1-ying.huang@intel.com 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> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> ---
--- a/mm/migrate.c~migrate_pages-silence-gcc-notes-for-mis-casting +++ a/mm/migrate.c @@ -1047,7 +1047,16 @@ static void __migrate_folio_extract(stru 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; _
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