Messages in this thread | | | Date | Fri, 30 Apr 2010 13:24:51 +0200 | From | Steffen Klassert <> | Subject | Re: [PATCH 7/8] padata: Flush the padata queues actively |
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On Thu, Apr 29, 2010 at 04:11:12PM -0700, Andrew Morton wrote: > On Thu, 29 Apr 2010 14:44:26 +0200 > Steffen Klassert <steffen.klassert@secunet.com> wrote: > > > +static void padata_flush_queues(struct parallel_data *pd) > > +{ > > + int cpu; > > + struct padata_queue *queue; > > + > > + for_each_cpu(cpu, pd->cpumask) { > > + queue = per_cpu_ptr(pd->queue, cpu); > > + flush_work(&queue->pwork); > > + } > > + > > + del_timer_sync(&pd->timer); > > + > > + if (atomic_read(&pd->reorder_objects)) > > + padata_reorder(pd); > > padata_reorder() can fail to do anything, if someone else is holding > pd->lock. What happens then? >
padata does not accept new objects for parallelization if padata_flush_queues is called. The way of the data objects throught the padata queues is
--> parallelization queue -> reorder queue -> serialization queue -->
So padata_flush_queues processes the objects in the parallelization queue by doing flush_work(&queue->pwork). Then we delete the timer and wait on a potentially running timer function. We are not accepting new objects and the parallelization queue is empty, so the lock must be free then.
> > > + for_each_cpu(cpu, pd->cpumask) { > > + queue = per_cpu_ptr(pd->queue, cpu); > > + flush_work(&queue->swork); > > + } > > + BUG_ON(atomic_read(&pd->refcnt) != 0); > > +} > > Are we safe against cpu hot-unplug in this code?
padata_flush_queues is called after a call to get_online_cpus in all but one cases. I just noticed that I forgot to add the get_online_cpus/put_online_cpus in padata_free. I'll update the get_online_cpus/put_online_cpus patch accordingly, then it should be save in all cases.
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