linux-kernel - Re: [PATCH v2 22/35] percpu-rwsem: enable percpu

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Date:   Mon, 31 Jan 2022 10:04:16 -0800
From:   Suren Baghdasaryan <surenb@...gle.com>
To:     Hillf Danton <hdanton@...a.com>
Cc:     Michel Lespinasse <michel@...pinasse.org>,
        Linux-MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 22/35] percpu-rwsem: enable percpu_sem destruction in
 atomic context

On Sat, Jan 29, 2022 at 4:13 AM Hillf Danton <hdanton@...a.com> wrote:
>
> On Fri, 28 Jan 2022 05:09:53 -0800 Michel Lespinasse wrote:
> > +
> > +static LIST_HEAD(destroy_list);
> > +static DEFINE_SPINLOCK(destroy_list_lock);
>
>    static bool destroyer_running;
>
> > +
> > +static void destroy_list_workfn(struct work_struct *work)
> > +{
> > +     struct percpu_rw_semaphore *sem, *sem2;
> > +     LIST_HEAD(to_destroy);
> > +
>
> again:
>
> > +     spin_lock(&destroy_list_lock);
>
>         if (list_empty(&destroy_list)) {
>                 destroyer_running = false;
>                 spin_unlock(&destroy_list_lock);
>                 return;
>         }
>         destroyer_running = true;
>
> > +     list_splice_init(&destroy_list, &to_destroy);
> > +     spin_unlock(&destroy_list_lock);
> > +
> > +     if (list_empty(&to_destroy))
> > +             return;
> > +
> > +     list_for_each_entry_safe(sem, sem2, &to_destroy, destroy_list_entry) {
>
>                 list_del(&sem->destroy_list_entry);
>
> > +             percpu_free_rwsem(sem);
> > +             kfree(sem);
> > +     }
>
>         goto again;
> > +}
> > +
> > +static DECLARE_WORK(destroy_list_work, destroy_list_workfn);
> > +
> > +void percpu_rwsem_async_destroy(struct percpu_rw_semaphore *sem)
> > +{
> > +     spin_lock(&destroy_list_lock);
> > +     list_add_tail(&sem->destroy_list_entry, &destroy_list);
> > +     spin_unlock(&destroy_list_lock);
> > +     schedule_work(&destroy_list_work);
>
> Nits
>         spin_lock(&destroy_list_lock);
> 1/      /* LIFO */
>         list_add(&sem->destroy_list_entry, &destroy_list);
> 2/      /* spawn worker if it is idle */
>         if (!destroyer_running)
> 3/              /* this is not critical work */
>                 queue_work(system_unbound_wq, &destroy_list_work);
>         spin_unlock(&destroy_list_lock);

Thanks for the review! Just to clarify, are you suggesting
simplifications to the current patch or do you see a function issue?

> > +}
> > --
> > 2.20.1
>