linux-kernel - Re: [PATCH v4 08/10] mm/vma: improve and document __is_vma_write

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Message-ID: <CAJuCfpG4JLu88YKZuRzprMgL3ZvCS+wLaeGbG_O4pKboBXxaVg@mail.gmail.com>
Date: Wed, 28 Jan 2026 10:52:37 -0800
From: Suren Baghdasaryan <surenb@...gle.com>
To: Vlastimil Babka <vbabka@...e.cz>
Cc: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, Andrew Morton <akpm@...ux-foundation.org>, 
	David Hildenbrand <david@...nel.org>, "Liam R . Howlett" <Liam.Howlett@...cle.com>, 
	Mike Rapoport <rppt@...nel.org>, 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 v4 08/10] mm/vma: improve and document __is_vma_write_locked()

On Wed, Jan 28, 2026 at 5:01 AM Vlastimil Babka <vbabka@...e.cz> wrote:
>
> On 1/28/26 12:51, Lorenzo Stoakes wrote:
> >>
> >> >
> >> > Thanks!
> >> >
> >> > >
> >> > > Few nits:
> >> > >
> >> > > > ---
> >> > > >  include/linux/mmap_lock.h | 44 ++++++++++++++++++++++-----------------
> >> > > >  1 file changed, 25 insertions(+), 19 deletions(-)
> >> > > >
> >> > > > diff --git a/include/linux/mmap_lock.h b/include/linux/mmap_lock.h
> >> > > > index 678f90080fa6..23bde4bd5a85 100644
> >> > > > --- a/include/linux/mmap_lock.h
> >> > > > +++ b/include/linux/mmap_lock.h
> >> > > > @@ -258,17 +258,30 @@ static inline void vma_end_read(struct vm_area_struct *vma)
> >> > > >     vma_refcount_put(vma);
> >> > > >  }
> >> > > >
> >> > > > -/* WARNING! Can only be used if mmap_lock is expected to be write-locked */
> >> > > > -static inline bool __is_vma_write_locked(struct vm_area_struct *vma, unsigned int *mm_lock_seq)
> >> > > > +static inline unsigned int __vma_raw_mm_seqnum(struct vm_area_struct *vma)
> >>
> >> This function returns the mm->mm_lock_seq.sequence attribute of mm, so
> >> no real commection to VMA. IMO it's better to rename it into
> >> __raw_mm_lock_seqnum(const struct mm_struct *mm) and have the callers
> >> pass vma->vm_mm.
> >
> > Sorry missed these comments.
> >
> > We are only ever referencing in terms of VMA's, so I think it makes sense still
> > to pass a VMA ptr, even if it just references vma->vm_mm.
>
> FWIW I agree.
>
> > I think the name of the function also makes things pretty clear, given it's
> > called essentially 'VMA['s] raw mm seqnum'.
> >
> >>
> >> > > >  {
> >> > > > +   const struct mm_struct *mm = vma->vm_mm;
> >> > > > +
> >> > > > +   /* We must hold an exclusive write lock for this access to be valid. */
> >> > > >     mmap_assert_write_locked(vma->vm_mm);
> >>
> >> If for some reason you need to keep this function VMA-centric, then in
> >> the above line please s/vma->vm_mm/mm
> >
> > Ah yeah, maybe if there's a respin? As kinda trivial thing, if that makes sense
> > to you!

Ack.

> >
> > Cheers, Lorenzo
>