linux-kernel - Re: [PATCH v8 11/16] mm: replace vm_lock and detached flag with a reference count

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Message-ID: <CAJuCfpGtGw+MdGH+NNb+zSZBeJ1ct5p98fV0oD6LFyHXMFwYLA@mail.gmail.com>
Date: Thu, 9 Jan 2025 08:01:03 -0800
From: Suren Baghdasaryan <surenb@...gle.com>
To: Hillf Danton <hdanton@...a.com>
Cc: peterz@...radead.org, lorenzo.stoakes@...cle.com, hannes@...xchg.org, 
	hughd@...gle.com, linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 11/16] mm: replace vm_lock and detached flag with a
 reference count

On Thu, Jan 9, 2025 at 2:36 AM Hillf Danton <hdanton@...a.com> wrote:
>
> On Wed,  8 Jan 2025 18:30:20 -0800 Suren Baghdasaryan <surenb@...gle.com>
> > +
> > +static inline void vma_refcount_put(struct vm_area_struct *vma)
> > +{
> > +     int oldcnt;
> > +
> > +     if (!__refcount_dec_and_test(&vma->vm_refcnt, &oldcnt)) {
> > +             rwsem_release(&vma->vmlock_dep_map, _RET_IP_);
>
> In up_read() rwsem is released reguardless wakeup, which is different
> than what is added here. Nit.

Good point. I'll send a fixup since it's a small change. Thanks!

>
> > +
> > +             if (is_vma_writer_only(oldcnt - 1))
> > +                     rcuwait_wake_up(&vma->vm_mm->vma_writer_wait);
> > +     }
> > +}
> ...
> > @@ -735,9 +773,10 @@ static inline bool vma_start_read(struct vm_area_struct *vma)
> >        * This pairs with RELEASE semantics in vma_end_write_all().
> >        */
> >       if (unlikely(vma->vm_lock_seq == raw_read_seqcount(&vma->vm_mm->mm_lock_seq))) {
> > -             up_read(&vma->vm_lock.lock);
> > +             vma_refcount_put(vma);
> >               return false;
> >       }
>
> void up_read(struct rw_semaphore *sem)
> {
>         rwsem_release(&sem->dep_map, _RET_IP_);
>         __up_read(sem);
> }
>