linux-kernel - Re: [PATCH 17/31] workqueue: implement attribute-based unbound worker

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Message-ID: <20130310125821.GG24522@htj.dyndns.org>
Date:	Sun, 10 Mar 2013 05:58:21 -0700
From:	Tejun Heo <tj@...nel.org>
To:	Lai Jiangshan <laijs@...fujitsu.com>
Cc:	linux-kernel@...r.kernel.org, axboe@...nel.dk, jmoyer@...hat.com,
	zab@...hat.com
Subject: Re: [PATCH 17/31] workqueue: implement attribute-based unbound
 worker_pool management

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
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