linux-kernel - Re: [PATCH v4 8/8] mm: Mark anonymous struct field of 'struct vm

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Message-ID: <CAKwvOd=B+tMi7-82Q8hEYnQ+BzkLDygOhMh6cQ2L+3SaL+F4tQ@mail.gmail.com>
Date:   Wed, 20 Jan 2021 10:27:04 -0800
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Will Deacon <will@...nel.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Jan Kara <jack@...e.cz>, Minchan Kim <minchan@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Vinayak Menon <vinmenon@...eaurora.org>,
        Hugh Dickins <hughd@...gle.com>,
        kernel-team <kernel-team@...roid.com>
Subject: Re: [PATCH v4 8/8] mm: Mark anonymous struct field of 'struct
 vm_fault' as 'const'

On Wed, Jan 20, 2021 at 9:36 AM Will Deacon <will@...nel.org> wrote:
>
> The fields of this struct are only ever read after being initialised, so
> mark it 'const' before somebody tries to modify it again.
>
> Cc: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Signed-off-by: Will Deacon <will@...nel.org>
> ---
>  include/linux/mm.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index e0f056753bef..7ff3d9817d38 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -514,7 +514,7 @@ static inline bool fault_flag_allow_retry_first(unsigned int flags)
>   * pgoff should be used in favour of virtual_address, if possible.
>   */
>  struct vm_fault {
> -       struct {
> +       const struct {
>                 struct vm_area_struct *vma;     /* Target VMA */
>                 gfp_t gfp_mask;                 /* gfp mask to be used for allocations */
>                 pgoff_t pgoff;                  /* Logical page offset based on vma */

Is there a difference between:

+       const struct {
+               struct vm_area_struct *vma;     /* Target VMA */
+               gfp_t gfp_mask;                 /* gfp mask to be used
for allocations */
+               pgoff_t pgoff;                  /* Logical page offset
based on vma */
+               unsigned long address;          /* Faulting virtual address */
+       };

vs

+       struct {
+               struct vm_area_struct * const vma;     /* Target VMA */
+               const gfp_t gfp_mask;                 /* gfp mask to
be used for allocations */
+               const pgoff_t pgoff;                  /* Logical page
offset based on vma */
+               const unsigned long address;          /* Faulting
virtual address */
+       };

ie. marking the members const vs the anonymous struct?  Does anything
need to change in the use of these structures?

> --
> 2.30.0.284.gd98b1dd5eaa7-goog
>


-- 
Thanks,
~Nick Desaulniers