mm/mmap: refactor mlock_future_check()

  In all but one instance, mlock_future_check() is treated as a boolean
function despite returning an error code. In one instance, this error code
is ignored and replaced with -ENOMEM.

This is confusing, and the inversion of true -> failure, false -> success
is not warranted. Convert the function to a bool, lightly refactor and
return true if the check passes, false if not.

Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com>
---
 mm/internal.h  |  4 ++--
 mm/mmap.c      | 33 +++++++++++++++++----------------
 mm/mremap.c    |  2 +-
 mm/secretmem.c |  2 +-
 4 files changed, 21 insertions(+), 20 deletions(-)
  

On Mon, 22 May 2023 09:24:12 +0100 Lorenzo Stoakes <lstoakes@gmail.com> wrote:

> In all but one instance, mlock_future_check() is treated as a boolean
> function despite returning an error code. In one instance, this error code
> is ignored and replaced with -ENOMEM.
> 
> This is confusing, and the inversion of true -> failure, false -> success
> is not warranted. Convert the function to a bool, lightly refactor and
> return true if the check passes, false if not.

Yup.

I don't think the name does a good job of conveying the
function's use.

> -	if (mlock_future_check(mm, vm_flags, len))
> +	if (!mlock_future_check(mm, vm_flags, len))
>  		return -EAGAIN;

	if (!may_mlock_future(...))

or

	if (!mlock_future_ok(...))

?
  

On Mon, May 22, 2023 at 01:28:51PM -0700, Andrew Morton wrote:
> On Mon, 22 May 2023 09:24:12 +0100 Lorenzo Stoakes <lstoakes@gmail.com> wrote:
>
> > In all but one instance, mlock_future_check() is treated as a boolean
> > function despite returning an error code. In one instance, this error code
> > is ignored and replaced with -ENOMEM.
> >
> > This is confusing, and the inversion of true -> failure, false -> success
> > is not warranted. Convert the function to a bool, lightly refactor and
> > return true if the check passes, false if not.
>
> Yup.
>
> I don't think the name does a good job of conveying the
> function's use.
>
> > -	if (mlock_future_check(mm, vm_flags, len))
> > +	if (!mlock_future_check(mm, vm_flags, len))
> >  		return -EAGAIN;
>
> 	if (!may_mlock_future(...))
>
> or
>
> 	if (!mlock_future_ok(...))
>
> ?
>
>

Yeah I struggled with this, because the check only triggers if VM_LOCKED. I was
originally toying with can_mlock_future() but of course, it also returns true if
!VM_LOCKED...

I think your suggestion of mlock_future_ok() works well, could you change it to
that? Thanks!
  

On Mon, 22 May 2023 21:34:31 +0100 Lorenzo Stoakes <lstoakes@gmail.com> wrote:

> On Mon, May 22, 2023 at 01:28:51PM -0700, Andrew Morton wrote:
> > On Mon, 22 May 2023 09:24:12 +0100 Lorenzo Stoakes <lstoakes@gmail.com> wrote:
> >
> > > In all but one instance, mlock_future_check() is treated as a boolean
> > > function despite returning an error code. In one instance, this error code
> > > is ignored and replaced with -ENOMEM.
> > >
> > > This is confusing, and the inversion of true -> failure, false -> success
> > > is not warranted. Convert the function to a bool, lightly refactor and
> > > return true if the check passes, false if not.
> >
> > Yup.
> >
> > I don't think the name does a good job of conveying the
> > function's use.
> >
> > > -	if (mlock_future_check(mm, vm_flags, len))
> > > +	if (!mlock_future_check(mm, vm_flags, len))
> > >  		return -EAGAIN;
> >
> > 	if (!may_mlock_future(...))
> >
> > or
> >
> > 	if (!mlock_future_ok(...))
> >
> > ?
> >
> >
> 
> Yeah I struggled with this, because the check only triggers if VM_LOCKED. I was
> originally toying with can_mlock_future() but of course, it also returns true if
> !VM_LOCKED...
> 
> I think your suggestion of mlock_future_ok() works well, could you change it to
> that? Thanks!

Sure.  I'll make it a separate patch.


From: Andrew Morton <akpm@linux-foundation.org>
Subject: mm/mlock: rename mlock_future_check() to mlock_future_ok()
Date: Mon May 22 01:52:10 PM PDT 2023

It is felt that the name mlock_future_check() is vague - it doesn't
particularly convey the function's operation.  mlock_future_ok() is a
clearer name for a predicate function.

Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Lorenzo Stoakes <lstoakes@gmail.com>
Cc: Mike Rapoport (IBM) <rppt@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/internal.h  |    2 +-
 mm/mmap.c      |    8 ++++----
 mm/mremap.c    |    2 +-
 mm/secretmem.c |    2 +-
 4 files changed, 7 insertions(+), 7 deletions(-)

--- a/mm/internal.h~mm-mlock-rename-mlock_future_check-to-mlock_future_ok
+++ a/mm/internal.h
@@ -576,7 +576,7 @@ extern long populate_vma_page_range(stru
 extern long faultin_vma_page_range(struct vm_area_struct *vma,
 				   unsigned long start, unsigned long end,
 				   bool write, int *locked);
-extern bool mlock_future_check(struct mm_struct *mm, unsigned long flags,
+extern bool mlock_future_ok(struct mm_struct *mm, unsigned long flags,
 			       unsigned long bytes);
 /*
  * mlock_vma_folio() and munlock_vma_folio():
--- a/mm/mmap.c~mm-mlock-rename-mlock_future_check-to-mlock_future_ok
+++ a/mm/mmap.c
@@ -182,7 +182,7 @@ static int check_brk_limits(unsigned lon
 	if (IS_ERR_VALUE(mapped_addr))
 		return mapped_addr;
 
-	return mlock_future_check(current->mm, current->mm->def_flags, len)
+	return mlock_future_ok(current->mm, current->mm->def_flags, len)
 		? 0 : -EAGAIN;
 }
 static int do_brk_flags(struct vma_iterator *vmi, struct vm_area_struct *brkvma,
@@ -1149,7 +1149,7 @@ static inline unsigned long round_hint_t
 	return hint;
 }
 
-bool mlock_future_check(struct mm_struct *mm, unsigned long flags,
+bool mlock_future_ok(struct mm_struct *mm, unsigned long flags,
 			unsigned long bytes)
 {
 	unsigned long locked_pages, limit_pages;
@@ -1275,7 +1275,7 @@ unsigned long do_mmap(struct file *file,
 		if (!can_do_mlock())
 			return -EPERM;
 
-	if (!mlock_future_check(mm, vm_flags, len))
+	if (!mlock_future_ok(mm, vm_flags, len))
 		return -EAGAIN;
 
 	if (file) {
@@ -1927,7 +1927,7 @@ static int acct_stack_growth(struct vm_a
 		return -ENOMEM;
 
 	/* mlock limit tests */
-	if (!mlock_future_check(mm, vma->vm_flags, grow << PAGE_SHIFT))
+	if (!mlock_future_ok(mm, vma->vm_flags, grow << PAGE_SHIFT))
 		return -ENOMEM;
 
 	/* Check to ensure the stack will not grow into a hugetlb-only region */
--- a/mm/mremap.c~mm-mlock-rename-mlock_future_check-to-mlock_future_ok
+++ a/mm/mremap.c
@@ -775,7 +775,7 @@ static struct vm_area_struct *vma_to_res
 	if (vma->vm_flags & (VM_DONTEXPAND | VM_PFNMAP))
 		return ERR_PTR(-EFAULT);
 
-	if (!mlock_future_check(mm, vma->vm_flags, new_len - old_len))
+	if (!mlock_future_ok(mm, vma->vm_flags, new_len - old_len))
 		return ERR_PTR(-EAGAIN);
 
 	if (!may_expand_vm(mm, vma->vm_flags,
--- a/mm/secretmem.c~mm-mlock-rename-mlock_future_check-to-mlock_future_ok
+++ a/mm/secretmem.c
@@ -125,7 +125,7 @@ static int secretmem_mmap(struct file *f
 	if ((vma->vm_flags & (VM_SHARED | VM_MAYSHARE)) == 0)
 		return -EINVAL;
 
-	if (!mlock_future_check(vma->vm_mm, vma->vm_flags | VM_LOCKED, len))
+	if (!mlock_future_ok(vma->vm_mm, vma->vm_flags | VM_LOCKED, len))
 		return -EAGAIN;
 
 	vm_flags_set(vma, VM_LOCKED | VM_DONTDUMP);
  

On 5/22/23 10:24, Lorenzo Stoakes wrote:
> In all but one instance, mlock_future_check() is treated as a boolean
> function despite returning an error code. In one instance, this error code
> is ignored and replaced with -ENOMEM.
> 
> This is confusing, and the inversion of true -> failure, false -> success
> is not warranted. Convert the function to a bool, lightly refactor and
> return true if the check passes, false if not.
> 
> Signed-off-by: Lorenzo Stoakes <lstoakes@gmail.com>

Acked-by: Vlastimil Babka <vbabka@suse.cz>

> ---
>  mm/internal.h  |  4 ++--
>  mm/mmap.c      | 33 +++++++++++++++++----------------
>  mm/mremap.c    |  2 +-
>  mm/secretmem.c |  2 +-
>  4 files changed, 21 insertions(+), 20 deletions(-)
> 
> diff --git a/mm/internal.h b/mm/internal.h
> index bb6542279599..66dd214b302a 100644
> --- a/mm/internal.h
> +++ b/mm/internal.h
> @@ -576,8 +576,8 @@ extern long populate_vma_page_range(struct vm_area_struct *vma,
>  extern long faultin_vma_page_range(struct vm_area_struct *vma,
>  				   unsigned long start, unsigned long end,
>  				   bool write, int *locked);
> -extern int mlock_future_check(struct mm_struct *mm, unsigned long flags,
> -			      unsigned long len);
> +extern bool mlock_future_check(struct mm_struct *mm, unsigned long flags,
> +			       unsigned long bytes);

This would have been good opportunity to drop the extern.