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[PATCH v5 11/12] mm: constify assert/test functions in mm.h

Max Kellermann posted 12 patches 3 months, 1 week ago
There is a newer version of this series
[PATCH v5 11/12] mm: constify assert/test functions in mm.h
Posted by Max Kellermann 3 months, 1 week ago 
For improved const-correctness.

We select certain assert and 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.

Signed-off-by: Max Kellermann <max.kellermann@ionos.com>
---
 include/linux/mm.h | 40 ++++++++++++++++++++--------------------
 1 file changed, 20 insertions(+), 20 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 23864c3519d6..4cca66ba8839 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -703,7 +703,7 @@ static inline void release_fault_lock(struct vm_fault *vmf)
 		mmap_read_unlock(vmf->vma->vm_mm);
 }
 
-static inline void assert_fault_locked(struct vm_fault *vmf)
+static inline void assert_fault_locked(struct vm_fault *const vmf)
 {
 	if (vmf->flags & FAULT_FLAG_VMA_LOCK)
 		vma_assert_locked(vmf->vma);
@@ -716,7 +716,7 @@ static inline void release_fault_lock(struct vm_fault *vmf)
 	mmap_read_unlock(vmf->vma->vm_mm);
 }
 
-static inline void assert_fault_locked(struct vm_fault *vmf)
+static inline void assert_fault_locked(const struct vm_fault *vmf)
 {
 	mmap_assert_locked(vmf->vma->vm_mm);
 }
@@ -859,7 +859,7 @@ static inline bool vma_is_initial_stack(const struct vm_area_struct *vma)
 		vma->vm_end >= vma->vm_mm->start_stack;
 }
 
-static inline bool vma_is_temporary_stack(struct vm_area_struct *vma)
+static inline bool vma_is_temporary_stack(const struct vm_area_struct *const vma)
 {
 	int maybe_stack = vma->vm_flags & (VM_GROWSDOWN | VM_GROWSUP);
 
@@ -873,7 +873,7 @@ static inline bool vma_is_temporary_stack(struct vm_area_struct *vma)
 	return false;
 }
 
-static inline bool vma_is_foreign(struct vm_area_struct *vma)
+static inline bool vma_is_foreign(const struct vm_area_struct *const vma)
 {
 	if (!current->mm)
 		return true;
@@ -884,7 +884,7 @@ static inline bool vma_is_foreign(struct vm_area_struct *vma)
 	return false;
 }
 
-static inline bool vma_is_accessible(struct vm_area_struct *vma)
+static inline bool vma_is_accessible(const struct vm_area_struct *const vma)
 {
 	return vma->vm_flags & VM_ACCESS_FLAGS;
 }
@@ -895,7 +895,7 @@ static inline bool is_shared_maywrite(vm_flags_t vm_flags)
 		(VM_SHARED | VM_MAYWRITE);
 }
 
-static inline bool vma_is_shared_maywrite(struct vm_area_struct *vma)
+static inline bool vma_is_shared_maywrite(const struct vm_area_struct *const vma)
 {
 	return is_shared_maywrite(vma->vm_flags);
 }
@@ -1839,7 +1839,7 @@ static inline struct folio *pfn_folio(unsigned long pfn)
 }
 
 #ifdef CONFIG_MMU
-static inline pte_t mk_pte(struct page *page, pgprot_t pgprot)
+static inline pte_t mk_pte(const struct page *page, pgprot_t pgprot)
 {
 	return pfn_pte(page_to_pfn(page), pgprot);
 }
@@ -1854,7 +1854,7 @@ static inline pte_t mk_pte(struct page *page, pgprot_t pgprot)
  *
  * Return: A page table entry suitable for mapping this folio.
  */
-static inline pte_t folio_mk_pte(struct folio *folio, pgprot_t pgprot)
+static inline pte_t folio_mk_pte(const struct folio *folio, pgprot_t pgprot)
 {
 	return pfn_pte(folio_pfn(folio), pgprot);
 }
@@ -1870,7 +1870,7 @@ static inline pte_t folio_mk_pte(struct folio *folio, pgprot_t pgprot)
  *
  * Return: A page table entry suitable for mapping this folio.
  */
-static inline pmd_t folio_mk_pmd(struct folio *folio, pgprot_t pgprot)
+static inline pmd_t folio_mk_pmd(const struct folio *folio, pgprot_t pgprot)
 {
 	return pmd_mkhuge(pfn_pmd(folio_pfn(folio), pgprot));
 }
@@ -1886,7 +1886,7 @@ static inline pmd_t folio_mk_pmd(struct folio *folio, pgprot_t pgprot)
  *
  * Return: A page table entry suitable for mapping this folio.
  */
-static inline pud_t folio_mk_pud(struct folio *folio, pgprot_t pgprot)
+static inline pud_t folio_mk_pud(const struct folio *folio, pgprot_t pgprot)
 {
 	return pud_mkhuge(pfn_pud(folio_pfn(folio), pgprot));
 }
@@ -3488,7 +3488,7 @@ struct vm_area_struct *vma_lookup(struct mm_struct *mm, unsigned long addr)
 	return mtree_load(&mm->mm_mt, addr);
 }
 
-static inline unsigned long stack_guard_start_gap(struct vm_area_struct *vma)
+static inline unsigned long stack_guard_start_gap(const struct vm_area_struct *const vma)
 {
 	if (vma->vm_flags & VM_GROWSDOWN)
 		return stack_guard_gap;
@@ -3500,7 +3500,7 @@ static inline unsigned long stack_guard_start_gap(struct vm_area_struct *vma)
 	return 0;
 }
 
-static inline unsigned long vm_start_gap(struct vm_area_struct *vma)
+static inline unsigned long vm_start_gap(const struct vm_area_struct *const vma)
 {
 	unsigned long gap = stack_guard_start_gap(vma);
 	unsigned long vm_start = vma->vm_start;
@@ -3511,7 +3511,7 @@ static inline unsigned long vm_start_gap(struct vm_area_struct *vma)
 	return vm_start;
 }
 
-static inline unsigned long vm_end_gap(struct vm_area_struct *vma)
+static inline unsigned long vm_end_gap(const struct vm_area_struct *const vma)
 {
 	unsigned long vm_end = vma->vm_end;
 
@@ -3523,7 +3523,7 @@ static inline unsigned long vm_end_gap(struct vm_area_struct *vma)
 	return vm_end;
 }
 
-static inline unsigned long vma_pages(struct vm_area_struct *vma)
+static inline unsigned long vma_pages(const struct vm_area_struct *const vma)
 {
 	return (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
 }
@@ -3540,7 +3540,7 @@ static inline struct vm_area_struct *find_exact_vma(struct mm_struct *mm,
 	return vma;
 }
 
-static inline bool range_in_vma(struct vm_area_struct *vma,
+static inline bool range_in_vma(const struct vm_area_struct *const vma,
 				unsigned long start, unsigned long end)
 {
 	return (vma && vma->vm_start <= start && end <= vma->vm_end);
@@ -3656,7 +3656,7 @@ static inline int vm_fault_to_errno(vm_fault_t vm_fault, int foll_flags)
  * Indicates whether GUP can follow a PROT_NONE mapped page, or whether
  * a (NUMA hinting) fault is required.
  */
-static inline bool gup_can_follow_protnone(struct vm_area_struct *vma,
+static inline bool gup_can_follow_protnone(const struct vm_area_struct *const vma,
 					   unsigned int flags)
 {
 	/*
@@ -3786,7 +3786,7 @@ static inline bool debug_guardpage_enabled(void)
 	return static_branch_unlikely(&_debug_guardpage_enabled);
 }
 
-static inline bool page_is_guard(struct page *page)
+static inline bool page_is_guard(const struct page *const page)
 {
 	if (!debug_guardpage_enabled())
 		return false;
@@ -3817,7 +3817,7 @@ static inline void debug_pagealloc_map_pages(struct page *page, int numpages) {}
 static inline void debug_pagealloc_unmap_pages(struct page *page, int numpages) {}
 static inline unsigned int debug_guardpage_minorder(void) { return 0; }
 static inline bool debug_guardpage_enabled(void) { return false; }
-static inline bool page_is_guard(struct page *page) { return false; }
+static inline bool page_is_guard(const struct page *const page) { return false; }
 static inline bool set_page_guard(struct zone *zone, struct page *page,
 			unsigned int order) { return false; }
 static inline void clear_page_guard(struct zone *zone, struct page *page,
@@ -3899,7 +3899,7 @@ void vmemmap_free(unsigned long start, unsigned long end,
 #endif
 
 #ifdef CONFIG_SPARSEMEM_VMEMMAP
-static inline unsigned long vmem_altmap_offset(struct vmem_altmap *altmap)
+static inline unsigned long vmem_altmap_offset(const struct vmem_altmap *altmap)
 {
 	/* number of pfns from base where pfn_to_page() is valid */
 	if (altmap)
@@ -3913,7 +3913,7 @@ static inline void vmem_altmap_free(struct vmem_altmap *altmap,
 	altmap->alloc -= nr_pfns;
 }
 #else
-static inline unsigned long vmem_altmap_offset(struct vmem_altmap *altmap)
+static inline unsigned long vmem_altmap_offset(const struct vmem_altmap *altmap)
 {
 	return 0;
 }
-- 
2.47.2
Re: [PATCH v5 11/12] mm: constify assert/test functions in mm.h
Posted by David Hildenbrand 3 months, 1 week ago 
On 01.09.25 14:30, Max Kellermann wrote:
> For improved const-correctness.
> 
> We select certain assert and 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.
> 
> Signed-off-by: Max Kellermann <max.kellermann@ionos.com>
> ---
>   include/linux/mm.h | 40 ++++++++++++++++++++--------------------
>   1 file changed, 20 insertions(+), 20 deletions(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 23864c3519d6..4cca66ba8839 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -703,7 +703,7 @@ static inline void release_fault_lock(struct vm_fault *vmf)
>   		mmap_read_unlock(vmf->vma->vm_mm);
>   }
>   
> -static inline void assert_fault_locked(struct vm_fault *vmf)
> +static inline void assert_fault_locked(struct vm_fault *const vmf)
>   {
>   	if (vmf->flags & FAULT_FLAG_VMA_LOCK)
>   		vma_assert_locked(vmf->vma);
> @@ -716,7 +716,7 @@ static inline void release_fault_lock(struct vm_fault *vmf)
>   	mmap_read_unlock(vmf->vma->vm_mm);
>   }
>   
> -static inline void assert_fault_locked(struct vm_fault *vmf)
> +static inline void assert_fault_locked(const struct vm_fault *vmf)
>   {

This confused me a bit: in the upper variant it's "*const" and here it's 
"const *".

There are multiple such cases here, which might imply that it is not 
"relatively trivial to const-ify them". :)

Did you miss to convert some of these cases properly, or is there a 
reason for this inconsistency?

-- 
Cheers

David / dhildenb
Re: [PATCH v5 11/12] mm: constify assert/test functions in mm.h
Posted by Max Kellermann 3 months, 1 week ago 
On Mon, Sep 1, 2025 at 4:07 PM David Hildenbrand <david@redhat.com> wrote:
> > -static inline void assert_fault_locked(struct vm_fault *vmf)
> > +static inline void assert_fault_locked(const struct vm_fault *vmf)
> >   {
>
> This confused me a bit: in the upper variant it's "*const" and here it's
> "const *".

That was indeed a mistake. Both should be "const*const".

> There are multiple such cases here, which might imply that it is not
> "relatively trivial to const-ify them". :)

I double-checked this patch and couldn't find any other such mistake.
Or do you mean the function vs prototype thing on parameter values?
Re: [PATCH v5 11/12] mm: constify assert/test functions in mm.h
Posted by David Hildenbrand 3 months, 1 week ago 
On 01.09.25 17:17, Max Kellermann wrote:
> On Mon, Sep 1, 2025 at 4:07 PM David Hildenbrand <david@redhat.com> wrote:
>>> -static inline void assert_fault_locked(struct vm_fault *vmf)
>>> +static inline void assert_fault_locked(const struct vm_fault *vmf)
>>>    {
>>
>> This confused me a bit: in the upper variant it's "*const" and here it's
>> "const *".
> 
> That was indeed a mistake. Both should be "const*const".
> 
>> There are multiple such cases here, which might imply that it is not
>> "relatively trivial to const-ify them". :)
> 
> I double-checked this patch and couldn't find any other such mistake.
> Or do you mean the function vs prototype thing on parameter values?

If there is a simple rule (declaration/definition), then it's trivial. 
Probably worth spelling out that rule somewhere (unless I missed it).

As raised in the other reply, not sure if we should just keep them in sync.

I'm, not the biggest fan of the *const in general here. I can see why 
Andrew suggested it, but only doing that for pointers is a bit weird. 
Anyhow, that discussion is likely happening elsewhere, and I don't think 
there is real harm when doing it, as long as we are consistent with what 
we're doing.

-- 
Cheers

David / dhildenb

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