Messages in this thread | | | From | Lai Jiangshan <> | Date | Tue, 30 Aug 2022 17:32:17 +0800 | Subject | Re: [PATCH] workqueue: Protects wq_unbound_cpumask with wq_pool_attach_mutex |
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On Sat, Aug 27, 2022 at 8:33 AM Tejun Heo <tj@kernel.org> wrote: > > Hello, > > On Thu, Aug 18, 2022 at 10:33:48PM +0800, Lai Jiangshan wrote: > > @@ -5342,6 +5344,11 @@ static int workqueue_apply_unbound_cpumask(void) > > apply_wqattrs_cleanup(ctx); > > } > > > > + if (!ret) { > > + mutex_lock(&wq_pool_attach_mutex); > > + cpumask_copy(wq_unbound_cpumask, unbound_cpumask); > > + mutex_unlock(&wq_pool_attach_mutex); > > Is this enough? Shouldn't the lock be protecting a wider scope? If there's > someone reading the flag with just pool_attach_mutex, what prevents them > reading it right before the new value is committed and keeps using the stale > value?
Which "flag"? wq_unbound_cpumask?
This code is adding protection for wq_unbound_cpumask and makes unbind_workers() use a stable version of wq_unbound_cpumask during operation.
It doesn't really matter if pool's mask becomes stale later again with respect to wq_unbound_cpumask.
No code ensures the disassociated pool's mask is kept with the newest wq_unbound_cpumask since the 10a5a651e3af ("workqueue: Restrict kworker in the offline CPU pool running on housekeeping CPUs") first uses wq_unbound_cpumask for the disassociated pools.
What matters is that the pool's mask should the wq_unbound_cpumask at the time when it becomes disassociated which has no isolated CPUs.
I don't like 10a5a651e3af for it not synching the pool's mask with wq_unbound_cpumask. But I think it works anyway.
> > Thanks. > > -- > tejun
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