linux-kernel - Re: [PATCH v5 06/12] mm, s390: constify mapping related test functions for improved const-correctness

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Message-ID: <8c19bd49-eb0b-4000-b3b3-afdb4af00341@lucifer.local>
Date: Mon, 1 Sep 2025 15:47:07 +0100
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: David Hildenbrand <david@...hat.com>
Cc: Max Kellermann <max.kellermann@...os.com>, akpm@...ux-foundation.org,
        axelrasmussen@...gle.com, yuanchu@...gle.com, willy@...radead.org,
        hughd@...gle.com, mhocko@...e.com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, Liam.Howlett@...cle.com, vbabka@...e.cz,
        rppt@...nel.org, surenb@...gle.com, vishal.moola@...il.com,
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Subject: Re: [PATCH v5 06/12] mm, s390: constify mapping related test
 functions for improved const-correctness

Not going to add too much noise as same points as David here :)

I'm still definitely leaning towards us not doing the double-const unless
thre's a good reason to or perhaps for larger functions.

But I'm open to being convinced otherwise :)

On Mon, Sep 01, 2025 at 03:54:25PM +0200, David Hildenbrand wrote:
> On 01.09.25 14:30, Max Kellermann wrote:
> > We select certain test functions which either invoke each other,
> > functions that are already const-ified, or no further functions.
> >
> > It is therefore relatively trivial to const-ify them, which
> > provides a basis for further const-ification further up the call
> > stack.
> >
> > (Even though seemingly unrelated, this also constifies the pointer
> > parameter of mmap_is_legacy() in arch/s390/mm/mmap.c because a copy of
> > the function exists in mm/util.c.)
> >
> > Signed-off-by: Max Kellermann <max.kellermann@...os.com>
> > Reviewed-by: Vishal Moola (Oracle) <vishal.moola@...il.com>
>
> Also here, some getters hiding.
>
> > ---
> >   arch/s390/mm/mmap.c     |  2 +-
> >   include/linux/mm.h      |  6 +++---
> >   include/linux/pagemap.h |  2 +-
> >   mm/util.c               | 11 ++++++-----
> >   4 files changed, 11 insertions(+), 10 deletions(-)
> >
> > diff --git a/arch/s390/mm/mmap.c b/arch/s390/mm/mmap.c
> > index 547104ccc22a..c0f619fb9ab3 100644
> > --- a/arch/s390/mm/mmap.c
> > +++ b/arch/s390/mm/mmap.c
> > @@ -27,7 +27,7 @@ static unsigned long stack_maxrandom_size(void)
> >   	return STACK_RND_MASK << PAGE_SHIFT;
> >   }
> > -static inline int mmap_is_legacy(struct rlimit *rlim_stack)
> > +static inline int mmap_is_legacy(const struct rlimit *const rlim_stack)
> >   {
> >   	if (current->personality & ADDR_COMPAT_LAYOUT)
> >   		return 1;
> > diff --git a/include/linux/mm.h b/include/linux/mm.h
> > index f70c6b4d5f80..23864c3519d6 100644
> > --- a/include/linux/mm.h
> > +++ b/include/linux/mm.h
> > @@ -986,7 +986,7 @@ static inline bool vma_is_shmem(const struct vm_area_struct *vma) { return false
> >   static inline bool vma_is_anon_shmem(const struct vm_area_struct *vma) { return false; }
> >   #endif
> > -int vma_is_stack_for_current(struct vm_area_struct *vma);
> > +int vma_is_stack_for_current(const struct vm_area_struct *vma);
>
> Should this also be *const ?
>
> >   /* flush_tlb_range() takes a vma, not a mm, and can care about flags */
> >   #define TLB_FLUSH_VMA(mm,flags) { .vm_mm = (mm), .vm_flags = (flags) }
> > @@ -2585,7 +2585,7 @@ void folio_add_pin(struct folio *folio);
> >   int account_locked_vm(struct mm_struct *mm, unsigned long pages, bool inc);
> >   int __account_locked_vm(struct mm_struct *mm, unsigned long pages, bool inc,
> > -			struct task_struct *task, bool bypass_rlim);
> > +			const struct task_struct *task, bool bypass_rlim);
>
>
> Dito.
>
> >   struct kvec;
> >   struct page *get_dump_page(unsigned long addr, int *locked);
> > @@ -3348,7 +3348,7 @@ void anon_vma_interval_tree_verify(struct anon_vma_chain *node);
> >   	     avc; avc = anon_vma_interval_tree_iter_next(avc, start, last))
> >   /* mmap.c */
> > -extern int __vm_enough_memory(struct mm_struct *mm, long pages, int cap_sys_admin);
> > +extern int __vm_enough_memory(const struct mm_struct *mm, long pages, int cap_sys_admin);
> >   extern int insert_vm_struct(struct mm_struct *, struct vm_area_struct *);
> >   extern void exit_mmap(struct mm_struct *);
> >   bool mmap_read_lock_maybe_expand(struct mm_struct *mm, struct vm_area_struct *vma,
> > diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
> > index 1d35f9e1416e..968b58a97236 100644
> > --- a/include/linux/pagemap.h
> > +++ b/include/linux/pagemap.h
> > @@ -551,7 +551,7 @@ static inline void filemap_nr_thps_dec(struct address_space *mapping)
> >   #endif
> >   }
> > -struct address_space *folio_mapping(struct folio *);
> > +struct address_space *folio_mapping(const struct folio *folio);
>
> And this one?
>
> --
> Cheers
>
> David / dhildenb
>