Remove XA_ZERO from error recovery of

[RFC PATCH 2/6] mm/mmap: Abstract vma clean up from exit_mmap()

Posted by Liam R. Howlett 1 month, 2 weeks ago

Create the new function tear_down_vmas() to remove a range of vmas.
exit_mmap() will be removing all the vmas.

This is necessary for future patches.

No functional changes intended.

Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
---
 mm/mmap.c | 37 ++++++++++++++++++++++++-------------
 1 file changed, 24 insertions(+), 13 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index c4c315b480af7..0995a48b46d59 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1250,6 +1250,29 @@ int vm_brk_flags(unsigned long addr, unsigned long request, vm_flags_t vm_flags)
 }
 EXPORT_SYMBOL(vm_brk_flags);
 
+static inline
+unsigned long tear_down_vmas(struct mm_struct *mm, struct vma_iterator *vmi,
+		struct vm_area_struct *vma, unsigned long max)
+{
+	unsigned long nr_accounted = 0;
+	int count = 0;
+
+	mmap_assert_write_locked(mm);
+	vma_iter_set(vmi, vma->vm_end);
+	do {
+		if (vma->vm_flags & VM_ACCOUNT)
+			nr_accounted += vma_pages(vma);
+		vma_mark_detached(vma);
+		remove_vma(vma);
+		count++;
+		cond_resched();
+		vma = vma_next(vmi);
+	} while (vma && vma->vm_end <= max);
+
+	BUG_ON(count != mm->map_count);
+	return nr_accounted;
+}
+
 /* Release all mmaps. */
 void exit_mmap(struct mm_struct *mm)
 {
@@ -1257,7 +1280,6 @@ void exit_mmap(struct mm_struct *mm)
 	struct vm_area_struct *vma;
 	unsigned long nr_accounted = 0;
 	VMA_ITERATOR(vmi, mm, 0);
-	int count = 0;
 
 	/* mm's last user has gone, and its about to be pulled down */
 	mmu_notifier_release(mm);
@@ -1297,18 +1319,7 @@ void exit_mmap(struct mm_struct *mm)
 	 * enabled, without holding any MM locks besides the unreachable
 	 * mmap_write_lock.
 	 */
-	vma_iter_set(&vmi, vma->vm_end);
-	do {
-		if (vma->vm_flags & VM_ACCOUNT)
-			nr_accounted += vma_pages(vma);
-		vma_mark_detached(vma);
-		remove_vma(vma);
-		count++;
-		cond_resched();
-		vma = vma_next(&vmi);
-	} while (vma && likely(!xa_is_zero(vma)));
-
-	BUG_ON(count != mm->map_count);
+	nr_accounted = tear_down_vmas(mm, &vmi, vma, ULONG_MAX);
 
 destroy:
 	__mt_destroy(&mm->mm_mt);
-- 
2.47.2

Re: [RFC PATCH 2/6] mm/mmap: Abstract vma clean up from exit_mmap()

Posted by Lorenzo Stoakes 1 month, 2 weeks ago

On Fri, Aug 15, 2025 at 03:10:27PM -0400, Liam R. Howlett wrote:
> Create the new function tear_down_vmas() to remove a range of vmas.
> exit_mmap() will be removing all the vmas.
>
> This is necessary for future patches.
>
> No functional changes intended.
>
> Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>

This function is pure and complete insanity, but this change looks
good. Couple nits below.

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

> ---
>  mm/mmap.c | 37 ++++++++++++++++++++++++-------------
>  1 file changed, 24 insertions(+), 13 deletions(-)
>
> diff --git a/mm/mmap.c b/mm/mmap.c
> index c4c315b480af7..0995a48b46d59 100644
> --- a/mm/mmap.c
> +++ b/mm/mmap.c
> @@ -1250,6 +1250,29 @@ int vm_brk_flags(unsigned long addr, unsigned long request, vm_flags_t vm_flags)
>  }
>  EXPORT_SYMBOL(vm_brk_flags);
>
> +static inline
> +unsigned long tear_down_vmas(struct mm_struct *mm, struct vma_iterator *vmi,
> +		struct vm_area_struct *vma, unsigned long max)
> +{
> +	unsigned long nr_accounted = 0;
> +	int count = 0;
> +
> +	mmap_assert_write_locked(mm);
> +	vma_iter_set(vmi, vma->vm_end);
> +	do {
> +		if (vma->vm_flags & VM_ACCOUNT)
> +			nr_accounted += vma_pages(vma);
> +		vma_mark_detached(vma);
> +		remove_vma(vma);
> +		count++;
> +		cond_resched();
> +		vma = vma_next(vmi);
> +	} while (vma && vma->vm_end <= max);
> +
> +	BUG_ON(count != mm->map_count);

Can we make this a WARN_ON() or WARN_ON_ONCE() while we're at it?

> +	return nr_accounted;
> +}
> +
>  /* Release all mmaps. */
>  void exit_mmap(struct mm_struct *mm)
>  {
> @@ -1257,7 +1280,6 @@ void exit_mmap(struct mm_struct *mm)
>  	struct vm_area_struct *vma;
>  	unsigned long nr_accounted = 0;

No need to initialise this to 0 any more.

>  	VMA_ITERATOR(vmi, mm, 0);
> -	int count = 0;
>
>  	/* mm's last user has gone, and its about to be pulled down */
>  	mmu_notifier_release(mm);
> @@ -1297,18 +1319,7 @@ void exit_mmap(struct mm_struct *mm)
>  	 * enabled, without holding any MM locks besides the unreachable
>  	 * mmap_write_lock.
>  	 */
> -	vma_iter_set(&vmi, vma->vm_end);
> -	do {
> -		if (vma->vm_flags & VM_ACCOUNT)
> -			nr_accounted += vma_pages(vma);
> -		vma_mark_detached(vma);
> -		remove_vma(vma);
> -		count++;
> -		cond_resched();
> -		vma = vma_next(&vmi);
> -	} while (vma && likely(!xa_is_zero(vma)));
> -
> -	BUG_ON(count != mm->map_count);
> +	nr_accounted = tear_down_vmas(mm, &vmi, vma, ULONG_MAX);
>
>  destroy:
>  	__mt_destroy(&mm->mm_mt);
> --
> 2.47.2
>

Re: [RFC PATCH 2/6] mm/mmap: Abstract vma clean up from exit_mmap()

Posted by Liam R. Howlett 1 month ago

* Lorenzo Stoakes <lorenzo.stoakes@oracle.com> [250819 14:38]:
> On Fri, Aug 15, 2025 at 03:10:27PM -0400, Liam R. Howlett wrote:
> > Create the new function tear_down_vmas() to remove a range of vmas.
> > exit_mmap() will be removing all the vmas.
> >
> > This is necessary for future patches.
> >
> > No functional changes intended.
> >
> > Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
> 
> This function is pure and complete insanity, but this change looks
> good. Couple nits below.
> 
> Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
> 
> > ---
> >  mm/mmap.c | 37 ++++++++++++++++++++++++-------------
> >  1 file changed, 24 insertions(+), 13 deletions(-)
> >
> > diff --git a/mm/mmap.c b/mm/mmap.c
> > index c4c315b480af7..0995a48b46d59 100644
> > --- a/mm/mmap.c
> > +++ b/mm/mmap.c
> > @@ -1250,6 +1250,29 @@ int vm_brk_flags(unsigned long addr, unsigned long request, vm_flags_t vm_flags)
> >  }
> >  EXPORT_SYMBOL(vm_brk_flags);
> >
> > +static inline
> > +unsigned long tear_down_vmas(struct mm_struct *mm, struct vma_iterator *vmi,
> > +		struct vm_area_struct *vma, unsigned long max)
> > +{
> > +	unsigned long nr_accounted = 0;
> > +	int count = 0;
> > +
> > +	mmap_assert_write_locked(mm);
> > +	vma_iter_set(vmi, vma->vm_end);
> > +	do {
> > +		if (vma->vm_flags & VM_ACCOUNT)
> > +			nr_accounted += vma_pages(vma);
> > +		vma_mark_detached(vma);
> > +		remove_vma(vma);
> > +		count++;
> > +		cond_resched();
> > +		vma = vma_next(vmi);
> > +	} while (vma && vma->vm_end <= max);
> > +
> > +	BUG_ON(count != mm->map_count);
> 
> Can we make this a WARN_ON() or WARN_ON_ONCE() while we're at it?

Sure!

> 
> > +	return nr_accounted;
> > +}
> > +
> >  /* Release all mmaps. */
> >  void exit_mmap(struct mm_struct *mm)
> >  {
> > @@ -1257,7 +1280,6 @@ void exit_mmap(struct mm_struct *mm)
> >  	struct vm_area_struct *vma;
> >  	unsigned long nr_accounted = 0;
> 
> No need to initialise this to 0 any more.

There is a goto label below that skips calling the tear down, so this is
still needed.

Thanks,
Liam

Re: [RFC PATCH 2/6] mm/mmap: Abstract vma clean up from exit_mmap()

Posted by Lorenzo Stoakes 4 weeks, 1 day ago

On Wed, Sep 03, 2025 at 03:56:03PM -0400, Liam R. Howlett wrote:
> * Lorenzo Stoakes <lorenzo.stoakes@oracle.com> [250819 14:38]:
> > On Fri, Aug 15, 2025 at 03:10:27PM -0400, Liam R. Howlett wrote:
> > > Create the new function tear_down_vmas() to remove a range of vmas.
> > > exit_mmap() will be removing all the vmas.
> > >
> > > This is necessary for future patches.
> > >
> > > No functional changes intended.
> > >
> > > Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
> >
> > This function is pure and complete insanity, but this change looks
> > good. Couple nits below.
> >
> > Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
> >
> > > ---
> > >  mm/mmap.c | 37 ++++++++++++++++++++++++-------------
> > >  1 file changed, 24 insertions(+), 13 deletions(-)
> > >
> > > diff --git a/mm/mmap.c b/mm/mmap.c
> > > index c4c315b480af7..0995a48b46d59 100644
> > > --- a/mm/mmap.c
> > > +++ b/mm/mmap.c
> > > @@ -1250,6 +1250,29 @@ int vm_brk_flags(unsigned long addr, unsigned long request, vm_flags_t vm_flags)
> > >  }
> > >  EXPORT_SYMBOL(vm_brk_flags);
> > >
> > > +static inline
> > > +unsigned long tear_down_vmas(struct mm_struct *mm, struct vma_iterator *vmi,
> > > +		struct vm_area_struct *vma, unsigned long max)
> > > +{
> > > +	unsigned long nr_accounted = 0;
> > > +	int count = 0;
> > > +
> > > +	mmap_assert_write_locked(mm);
> > > +	vma_iter_set(vmi, vma->vm_end);
> > > +	do {
> > > +		if (vma->vm_flags & VM_ACCOUNT)
> > > +			nr_accounted += vma_pages(vma);
> > > +		vma_mark_detached(vma);
> > > +		remove_vma(vma);
> > > +		count++;
> > > +		cond_resched();
> > > +		vma = vma_next(vmi);
> > > +	} while (vma && vma->vm_end <= max);
> > > +
> > > +	BUG_ON(count != mm->map_count);
> >
> > Can we make this a WARN_ON() or WARN_ON_ONCE() while we're at it?
>
> Sure!

Thanks :)

>
> >
> > > +	return nr_accounted;
> > > +}
> > > +
> > >  /* Release all mmaps. */
> > >  void exit_mmap(struct mm_struct *mm)
> > >  {
> > > @@ -1257,7 +1280,6 @@ void exit_mmap(struct mm_struct *mm)
> > >  	struct vm_area_struct *vma;
> > >  	unsigned long nr_accounted = 0;
> >
> > No need to initialise this to 0 any more.
>
> There is a goto label below that skips calling the tear down, so this is
> still needed.

Ah yeah, sorry missed the goto destroy there. No worries then :)

>
> Thanks,
> Liam