Re: [PATCH RESEND v3 09/10] mm/vma: update vma_assert_locked() to use lockdep

Lorenzo Stoakes
2026-01-23T18:51:13Z

On Fri, Jan 23, 2026 at 05:55:58PM +0100, Vlastimil Babka wrote:
> On 1/22/26 14:02, Lorenzo Stoakes wrote:
> > +/**
> > + * 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.
> > + */
> > static inline void vma_assert_locked(struct vm_area_struct *vma)
> > {
> > - unsigned int mm_lock_seq;
> > + unsigned int refs;
> >
> > /*
> > * See the comment describing the vm_area_struct->vm_refcnt field for
> > * details of possible refcnt values.
> > */
> > - VM_BUG_ON_VMA(refcount_read(&vma->vm_refcnt) <= 1 &&
> > - !__is_vma_write_locked(vma, &mm_lock_seq), vma);
> > +
> > + /*
> > + * If read-locked or currently excluding readers, then the VMA is
> > + * locked.
> > + */
> > +#ifdef CONFIG_LOCKDEP
> > + if (lock_is_held(&vma->vmlock_dep_map))
> > + return;
> > +#endif
> > +
> > + refs = refcount_read(&vma->vm_refcnt);
> > +
> > + /*
> > + * In this case we're either read-locked, write-locked with temporary
> > + * readers, or in the midst of excluding readers, all of which means
> > + * we're locked.
> > + */
> > + if (refs > 1)
> > + return;
> > +
> > + /* It is a bug for the VMA to be detached here. */
> > + VM_BUG_ON_VMA(!refs, vma);
> > +
>
> Yeah previously this function was all VM_BUG_ON() but since that's now
> frowned upon, can we not do it anymore?
> Seem we do have VM_WARN_ON_ONCE_VMA().

Ack yeah will replace! Already replaced some in previous patch also :)

>
> > + /*
> > + * OK, the VMA has a reference count of 1 which means it is either
> > + * unlocked and attached or write-locked, so assert that it is
> > + * write-locked.
> > + */
> > + vma_assert_write_locked(vma);
> > }
> >
> > static inline bool vma_is_attached(struct vm_area_struct *vma)
> > --
> > 2.52.0
>