Re: [PATCH 2/3] mm: only assert VMA locks if CONFIG_DEBUG_VM is set

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential
issue to consider:
- [Low] mm: missing CONFIG_DEBUG_VM guard in vma_assert_stabilised()
--

commit f772b5a674b87f589a1f2a31923e1ad5204e14f7
Author: Lorenzo Stoakes (ARM) <ljs@kernel.org>

mm: only assert VMA locks if CONFIG_DEBUG_VM is set

This commit gates VMA lock and attachment assertions on CONFIG_DEBUG_VM so
that they do not run in non-debug builds.

> diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h
> index 7b6749e0f6fa6..d0291e6a4d20d 100644
> --- a/include/linux/mmap_lock.h
> +++ b/include/linux/mmap_lock.h

[ ... ]

> @@ -369,11 +374,16 @@ static inline void vma_assert_write_locked(const struct vm_area_struct *vma)
>   * vma_assert_locked() - assert that @vma holds either a VMA read or a VMA write
>   * lock and is not detached.
>   * @vma: The VMA to assert.
> + *
> + * Assert only if CONFIG_DEBUG_VM is set.
>   */
>  static inline void vma_assert_locked(const struct vm_area_struct *vma)
>  {
>  	unsigned int refcnt;
>  
> +	if (!IS_ENABLED(CONFIG_DEBUG_VM))
> +		return;
> +
>  	if (!IS_ENABLED(CONFIG_MMU)) {
>  		mmap_assert_locked(vma->vm_mm);
>  		return;

[Severity: Low]
Should vma_assert_stabilised() also return early when
!IS_ENABLED(CONFIG_DEBUG_VM), just like vma_assert_can_modify() below?

Because its tail call to vma_assert_locked() is now a no-op when
CONFIG_DEBUG_VM is disabled, vma_assert_stabilised() can no longer assert
anything in !CONFIG_DEBUG_VM builds, but it still runs lockdep_is_held()
or the volatile atomic_long_read() in rwsem_is_locked(&vma->vm_mm->mmap_lock)
(and vma_has_anon_rmap() still runs the volatile refcount_read() in
vma_is_attached(vma) before calling it):

include/linux/mmap_lock.h:vma_assert_stabilised() {
	...
	if (IS_ENABLED(CONFIG_LOCKDEP)) {
		if (lockdep_is_held(&vma->vm_mm->mmap_lock))
			return;
	} else {
		if (rwsem_is_locked(&vma->vm_mm->mmap_lock))
			return;
	}

	vma_assert_locked(vma);
}

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261110-tame-vma-asserts-v1-0-be293ff499a7@kernel.org?part=2