From:   "Huang, Ying" <ying.huang@intel.com>
To:     Linus Torvalds <torvalds@linux-foundation.org>
Cc:     Andrew Morton <akpm@linux-foundation.org>, Jan Kara <jack@suse.cz>,
        Vishal Moola <vishal.moola@gmail.com>,
        Paulo Alcantara <pc@cjr.nz>,
        Matthew Wilcox <willy@infradead.org>,
        David Howells <dhowells@redhat.com>,
        Steve French <stfrench@microsoft.com>,
        Baolin Wang <baolin.wang@linux.alibaba.com>,
        Xin Hao <xhao@linux.alibaba.com>, linux-mm@kvack.org,
        mm-commits@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [GIT PULL] MM updates for 6.3-rc1
References: <20230220135225.91b0f28344c01d5306c31230@linux-foundation.org>
        <CAHk-=whAAOVBrzwb2uMjCmdRrtudGesYj0tuqdUgi8X_gbw1jw@mail.gmail.com>
Date:   Fri, 24 Feb 2023 11:01:49 +0800
In-Reply-To: <CAHk-=whAAOVBrzwb2uMjCmdRrtudGesYj0tuqdUgi8X_gbw1jw@mail.gmail.com>
        (Linus Torvalds's message of "Thu, 23 Feb 2023 17:33:37 -0800")
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Linus Torvalds <torvalds@linux-foundation.org> writes:

>
>  - gcc 12.2.1 quite reasonable complains about some of the new MM code:
>
>     mm/migrate.c: In function =E2=80=98__migrate_folio_extract=E2=80=99:
>     mm/migrate.c:1050:20: note: randstruct: casting between randomized
> structure pointer types (ssa): =E2=80=98struct anon_vma=E2=80=99 and =E2=
=80=98struct
> address_space=E2=80=99
>
>      1050 |         *anon_vmap =3D (void *)dst->mapping;
>           |         ~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~
>
>    and while this doesn't cause a build failure ("note" is different
> from "warning"), I do think something needs to be done. Gcc is right.
> This code seems to *work* simply because it's intentionally
> mis-casting pointers,

Yes.  The mis-casting is intentional.  I just need some place to hold
the data temporarily (save in __migrate_folio_record() and clear in
__migrate_folio_extract()).  And "dst" is newly allocated folio.

> but I think it needs to be seriously looked at and something done to
> make gcc happy (and a *LARGE* comment about it).

Sure.  I will check whether there's some way to make gcc happy and add
some comments about that.  There's some comments for
__migrate_folio_extract(), but that's isn't enough apprently.)

> That last note is not some merge result, it's purely about the new MM cod=
e.
>

[snip]

Best Regards,
Huang, Ying