Re: [PATCH 17/31] workqueue: implement attribute-based unbound worker_pool management

Tejun Heo
2013-03-10T12:58:26Z

On Sun, Mar 10, 2013 at 06:08:57PM +0800, Lai Jiangshan wrote:
> > @@ -3185,12 +3250,133 @@ static int init_worker_pool(struct worker_pool *pool)
> > mutex_init(&pool->assoc_mutex);
> > ida_init(&pool->worker_ida);
> >
> > + INIT_HLIST_NODE(&pool->hash_node);
> > + atomic_set(&pool->refcnt, 1);
>
> We should document: the code before "atomic_set(&pool->refcnt, 1);" should not failed.
> (In case we add failable code before it when we forget this requirement in future".
> reason: when get_unbound_pool() fails, we expected ->refcnt = 1)

Yeap, comments added.

> > +/**
> > + * put_unbound_pool - put a worker_pool
> > + * @pool: worker_pool to put
> > + *
> > + * Put @pool. If its refcnt reaches zero, it gets destroyed in sched-RCU
> > + * safe manner.
> > + */
> > +static void put_unbound_pool(struct worker_pool *pool)
> > +{
> > + struct worker *worker;
> > +
> > + if (!atomic_dec_and_test(&pool->refcnt))
> > + return;
>
> if get_unbound_pool() happens here, it will get a destroyed pool.
> so we need to move "spin_lock_irq(&workqueue_lock);" before above statement.
> (and ->refcnt don't need atomic after moved)

Hmmm... right. Nice catch. Updating...

> > + if (WARN_ON(pool->nr_workers != pool->nr_idle))
> > + return;
>
> This can be false-negative. we should remove this WARN_ON().

How would the test fail spuriously? Can you please elaborate?

Thanks.

--
tejun