linux-kernel - Re: [PATCH v4 03/10] mm/vma: rename is_vma_write

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Message-ID: <97d33d7a-66f6-45be-995d-04247d514c39@lucifer.local>
Date: Mon, 26 Jan 2026 09:45:30 +0000
From: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
To: Suren Baghdasaryan <surenb@...gle.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
        David Hildenbrand <david@...nel.org>,
        "Liam R . Howlett" <Liam.Howlett@...cle.com>,
        Vlastimil Babka <vbabka@...e.cz>, 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 03/10] mm/vma: rename is_vma_write_only(), separate
 out shared refcount put

On Sun, Jan 25, 2026 at 09:36:19PM -0800, Suren Baghdasaryan wrote:
> On Fri, Jan 23, 2026 at 12:12 PM Lorenzo Stoakes
> <lorenzo.stoakes@...cle.com> wrote:
> >
> > The is_vma_writer_only() function is misnamed - this isn't determining if
> > there is only a write lock, as it checks for the presence of the
> > VM_REFCNT_EXCLUDE_READERS_FLAG.
> >
> > Really, it is checking to see whether readers are excluded, with a
> > possibility of a false positive in the case of a detachment (there we
> > expect the vma->vm_refcnt to eventually be set to
> > VM_REFCNT_EXCLUDE_READERS_FLAG, whereas for an attached VMA we expect it to
> > eventually be set to VM_REFCNT_EXCLUDE_READERS_FLAG + 1).
> >
> > Rename the function accordingly.
> >
> > Relatedly, we use a __refcount_dec_and_test() primitive directly in
> > vma_refcount_put(), using the old value to determine what the reference
> > count ought to be after the operation is complete (ignoring racing
> > reference count adjustments).
> >
> > Wrap this into a __vma_refcount_put_return() function, which we can then
> > utilise in vma_mark_detached() and thus keep the refcount primitive usage
> > abstracted.
> >
> > This function, as the name implies, returns the value after the reference
> > count has been updated.
> >
> > This reduces duplication in the two invocations of this function.
> >
> > Also adjust comments, removing duplicative comments covered elsewhere and
> > adding more to aid understanding.
> >
> > No functional change intended.
> >
> > Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@...cle.com>
>
> Reviewed-by: Suren Baghdasaryan <surenb@...gle.com>

Thanks!