On Wed, 3 Dec 2014 23:31:16 +0100 Dongsu Park <dongsu.park@profitbricks.com>
wrote:

> Hi Tejun,
> 
> On 03.12.2014 13:02, Tejun Heo wrote:
> > So, something like the following.  Only compile tested.  I'll test it
> > and post proper patches w/ due credits.
> 
> I have been already satisfied with Neil's patch,
> but your patch looks indeed a lot cleaner, I like it.
> I just compiled and tested it shortly, which seems to work.
> Though there's one nitpick. (see below)
> 
> > Thanks.
> > 
> > Index: work/kernel/workqueue.c
> > ===================================================================
> > --- work.orig/kernel/workqueue.c
> > +++ work/kernel/workqueue.c
> > @@ -1804,8 +1804,8 @@ static void pool_mayday_timeout(unsigned
> >  	struct worker_pool *pool = (void *)__pool;
> >  	struct work_struct *work;
> >  
> > -	spin_lock_irq(&wq_mayday_lock);		/* for wq->maydays */
> > -	spin_lock(&pool->lock);
> > +	spin_lock_irq(&pool->lock);
> > +	spin_lock(&wq_mayday_lock);		/* for wq->maydays */
> >  
> >  	if (need_to_create_worker(pool)) {
> >  		/*
> > @@ -1818,8 +1818,8 @@ static void pool_mayday_timeout(unsigned
> >  			send_mayday(work);
> >  	}
> >  
> > -	spin_unlock(&pool->lock);
> > -	spin_unlock_irq(&wq_mayday_lock);
> > +	spin_unlock(&wq_mayday_lock);
> > +	spin_unlock_irq(&pool->lock);
> >  
> >  	mod_timer(&pool->mayday_timer, jiffies + MAYDAY_INTERVAL);
> >  }
> > @@ -2248,12 +2248,29 @@ repeat:
> >  		 * Slurp in all works issued via this workqueue and
> >  		 * process'em.
> >  		 */
> > -		WARN_ON_ONCE(!list_empty(&rescuer->scheduled));
> > +		WARN_ON_ONCE(!list_empty(scheduled));
> >  		list_for_each_entry_safe(work, n, &pool->worklist, entry)
> >  			if (get_work_pwq(work) == pwq)
> >  				move_linked_works(work, scheduled, &n);
> >  
> > -		process_scheduled_works(rescuer);
> > +		if (!list_empty(scheduled)) {
> > +			process_scheduled_works(rescuer);
> > +
> > +			/*
> > +			 * The above execution of rescued work items could
> > +			 * have created more to rescue through
> > +			 * pwq_activate_first_delayed() or chained
> > +			 * queueing.  Let's put @pwq back on mayday list so
> > +			 * that such back-to-back work items, which may be
> > +			 * being used to relieve memory pressure, don't
> > +			 * incur MAYDAY_INTERVAL delay inbetween.
> > +			 */
> > +			if (need_to_create_worker(pool)) {
> > +				spin_lock(&wq_mayday_lock);
> 
> Does it need to call get_pwq(pwq), doesn't it?

Yes, I think it does.

Swapping the order of the locks make it so much nicer, doesn't it!!

Thanks,
NeilBrown


> 
> Thanks,
> Dongsu
> 
> > +				list_move_tail(&pwq->mayday_node, &wq->maydays);
> > +				spin_unlock(&wq_mayday_lock);
> > +			}
> > +		}
> >  
> >  		/*
> >  		 * Put the reference grabbed by send_mayday().  @pool won't
> > 
> > -- 
> > tejun