Re: [PATCH v6 08/12] mm: constify arch_pick_mmap_layout() for improved const-correctness

[Lorenzo Stoakes <lorenzo.stoakes@oracle.com>]

On Mon, Sep 01, 2025 at 10:50:17PM +0200, Max Kellermann wrote:
> This function only reads from the rlimit pointer (but writes to the
> mm_struct pointer which is kept without `const`).
>
> All callees are already const-ified or (internal functions) are being
> constified by this patch.
>
> Signed-off-by: Max Kellermann <max.kellermann@ionos.com>
> Reviewed-by: Vishal Moola (Oracle) <vishal.moola@gmail.com>

LGTM, so:

Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>

> ---
>  arch/s390/mm/mmap.c              | 4 ++--
>  arch/sparc/kernel/sys_sparc_64.c | 2 +-
>  arch/x86/mm/mmap.c               | 6 +++---
>  include/linux/sched/mm.h         | 4 ++--
>  mm/util.c                        | 6 +++---
>  5 files changed, 11 insertions(+), 11 deletions(-)
>
> diff --git a/arch/s390/mm/mmap.c b/arch/s390/mm/mmap.c
> index e188cb6d4946..197c1d9497a7 100644
> --- a/arch/s390/mm/mmap.c
> +++ b/arch/s390/mm/mmap.c
> @@ -47,7 +47,7 @@ static unsigned long mmap_base_legacy(unsigned long rnd)
>  }
>
>  static inline unsigned long mmap_base(unsigned long rnd,
> -				      struct rlimit *rlim_stack)
> +				      const struct rlimit *rlim_stack)
>  {
>  	unsigned long gap = rlim_stack->rlim_cur;
>  	unsigned long pad = stack_maxrandom_size() + stack_guard_gap;
> @@ -169,7 +169,7 @@ unsigned long arch_get_unmapped_area_topdown(struct file *filp, unsigned long ad
>   * This function, called very early during the creation of a new
>   * process VM image, sets up which VM layout function to use:
>   */
> -void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
> +void arch_pick_mmap_layout(struct mm_struct *mm, const struct rlimit *rlim_stack)
>  {
>  	unsigned long random_factor = 0UL;
>
> diff --git a/arch/sparc/kernel/sys_sparc_64.c b/arch/sparc/kernel/sys_sparc_64.c
> index 785e9909340f..55faf2effa46 100644
> --- a/arch/sparc/kernel/sys_sparc_64.c
> +++ b/arch/sparc/kernel/sys_sparc_64.c
> @@ -294,7 +294,7 @@ static unsigned long mmap_rnd(void)
>  	return rnd << PAGE_SHIFT;
>  }
>
> -void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
> +void arch_pick_mmap_layout(struct mm_struct *mm, const struct rlimit *rlim_stack)
>  {
>  	unsigned long random_factor = mmap_rnd();
>  	unsigned long gap;
> diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c
> index 708f85dc9380..82f3a987f7cf 100644
> --- a/arch/x86/mm/mmap.c
> +++ b/arch/x86/mm/mmap.c
> @@ -80,7 +80,7 @@ unsigned long arch_mmap_rnd(void)
>  }
>
>  static unsigned long mmap_base(unsigned long rnd, unsigned long task_size,
> -			       struct rlimit *rlim_stack)
> +			       const struct rlimit *rlim_stack)
>  {
>  	unsigned long gap = rlim_stack->rlim_cur;
>  	unsigned long pad = stack_maxrandom_size(task_size) + stack_guard_gap;
> @@ -110,7 +110,7 @@ static unsigned long mmap_legacy_base(unsigned long rnd,
>   */
>  static void arch_pick_mmap_base(unsigned long *base, unsigned long *legacy_base,
>  		unsigned long random_factor, unsigned long task_size,
> -		struct rlimit *rlim_stack)
> +		const struct rlimit *rlim_stack)
>  {
>  	*legacy_base = mmap_legacy_base(random_factor, task_size);
>  	if (mmap_is_legacy())
> @@ -119,7 +119,7 @@ static void arch_pick_mmap_base(unsigned long *base, unsigned long *legacy_base,
>  		*base = mmap_base(random_factor, task_size, rlim_stack);
>  }
>
> -void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
> +void arch_pick_mmap_layout(struct mm_struct *mm, const struct rlimit *rlim_stack)
>  {
>  	if (mmap_is_legacy())
>  		mm_flags_clear(MMF_TOPDOWN, mm);
> diff --git a/include/linux/sched/mm.h b/include/linux/sched/mm.h
> index 2201da0afecc..0232d983b715 100644
> --- a/include/linux/sched/mm.h
> +++ b/include/linux/sched/mm.h
> @@ -178,7 +178,7 @@ static inline void mm_update_next_owner(struct mm_struct *mm)
>  #endif
>
>  extern void arch_pick_mmap_layout(struct mm_struct *mm,
> -				  struct rlimit *rlim_stack);
> +				  const struct rlimit *rlim_stack);
>
>  unsigned long
>  arch_get_unmapped_area(struct file *filp, unsigned long addr,
> @@ -211,7 +211,7 @@ generic_get_unmapped_area_topdown(struct file *filp, unsigned long addr,
>  				  unsigned long flags, vm_flags_t vm_flags);
>  #else
>  static inline void arch_pick_mmap_layout(struct mm_struct *mm,
> -					 struct rlimit *rlim_stack) {}
> +					 const struct rlimit *rlim_stack) {}
>  #endif
>
>  static inline bool in_vfork(struct task_struct *tsk)
> diff --git a/mm/util.c b/mm/util.c
> index 241d2eaf26ca..77462027ad24 100644
> --- a/mm/util.c
> +++ b/mm/util.c
> @@ -431,7 +431,7 @@ static int mmap_is_legacy(const struct rlimit *rlim_stack)
>  #define MIN_GAP		(SZ_128M)
>  #define MAX_GAP		(STACK_TOP / 6 * 5)
>
> -static unsigned long mmap_base(unsigned long rnd, struct rlimit *rlim_stack)
> +static unsigned long mmap_base(const unsigned long rnd, const struct rlimit *rlim_stack)
>  {
>  #ifdef CONFIG_STACK_GROWSUP
>  	/*
> @@ -462,7 +462,7 @@ static unsigned long mmap_base(unsigned long rnd, struct rlimit *rlim_stack)
>  #endif
>  }
>
> -void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
> +void arch_pick_mmap_layout(struct mm_struct *mm, const struct rlimit *rlim_stack)
>  {
>  	unsigned long random_factor = 0UL;
>
> @@ -478,7 +478,7 @@ void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
>  	}
>  }
>  #elif defined(CONFIG_MMU) && !defined(HAVE_ARCH_PICK_MMAP_LAYOUT)
> -void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
> +void arch_pick_mmap_layout(struct mm_struct *mm, const struct rlimit *rlim_stack)
>  {
>  	mm->mmap_base = TASK_UNMAPPED_BASE;
>  	mm_flags_clear(MMF_TOPDOWN, mm);
> --
> 2.47.2
>