On Mon, Jan 31, 2022 at 6:10 PM Hillf Danton <hdanton@xxxxxxxx> wrote:
>
> On Mon, 31 Jan 2022 10:04:16 -0800 Suren Baghdasaryan wrote:
> > On Sat, Jan 29, 2022 at 4:13 AM Hillf Danton 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?
>
> Apart from the nits that can be safely ignored in usual spins, I wonder if
> the async destroy can be used in the contexts wrt raw_spin_lock.
>
> Hillf
>
> raw_spin_lock_irq(&foo->lock);
> ...
> percpu_rwsem_async_destroy(*sem);
> ...
> raw_spin_unlock_irq(&foo->lock);
Sorry for the delay. Are you concerned about the use of spin_lock()
inside percpu_rwsem_async_destroy() which would become a sleeping lock
in case of PREEMPT_RT? If so, we can use raw_spin_lock() when locking
destroy_list_lock. Please confirm. Thanks!
>
