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

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Message-ID: <bae98030-f359-49e7-b294-14aec5a5425e@suse.cz>
Date: Wed, 28 Jan 2026 14:01:42 +0100
From: Vlastimil Babka <vbabka@...e.cz>
To: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>,
 Suren Baghdasaryan <surenb@...gle.com>
Cc: 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 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!
> 
> Cheers, Lorenzo