Messages in this thread | | | From | Valentin Schneider <> | Subject | Re: [PATCH -v3 5/9] workqueue: Tag bound workers with KTHREAD_IS_PER_CPU | Date | Thu, 21 Jan 2021 14:31:20 +0000 |
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On 21/01/21 11:17, Peter Zijlstra wrote: > @@ -4972,9 +4977,11 @@ static void rebind_workers(struct worker > * of all workers first and then clear UNBOUND. As we're called > * from CPU_ONLINE, the following shouldn't fail. > */ > - for_each_pool_worker(worker, pool) > + for_each_pool_worker(worker, pool) { > + kthread_set_per_cpu(worker->task, pool->cpu); > WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task, > pool->attrs->cpumask) < 0);
At the end of this series, is_cpu_allowed() allows kthreads with KTHREAD_IS_PER_CPU on any online CPU, even if it isn't the designated kthread->cpu.
I thought there might be a race here, given this gives us a window where a pcpu kworker has the flag but is still affined to cpus_possible_mask. Now, given cpus_write_lock(), we can't have a CPU going up while another goes down. So I think it's actually fine, and I've been chasing ghosts yet again.
> + } > > raw_spin_lock_irq(&pool->lock); >
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