linux-kernel - Re: [PATCH RESEND v3 09/10] mm/vma: update vma_assert

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Message-ID: <899d1fa9-ffe0-4c37-b1f4-01547c3423da@lucifer.local>
Date: Fri, 23 Jan 2026 18:49:56 +0000
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...nel.org>,
        "Liam R . Howlett" <Liam.Howlett@...cle.com>,
        Mike Rapoport <rppt@...nel.org>,
        Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>,
        Shakeel Butt <shakeel.butt@...ux.dev>, Jann Horn <jannh@...gle.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-rt-devel@...ts.linux.dev, Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Boqun Feng <boqun.feng@...il.com>, Waiman Long <longman@...hat.com>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Clark Williams <clrkwllms@...nel.org>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH RESEND v3 09/10] mm/vma: update vma_assert_locked() to
 use lockdep

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
>