On 13/01/21 21:28, Lai Jiangshan wrote:
> On Tue, Jan 12, 2021 at 10:51 PM Peter Zijlstra <[email protected]> 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) {
>> WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task,
>> pool->attrs->cpumask) < 0);
>> + kthread_set_per_cpu(worker->task, true);
>
> Will the schedule break affinity in the middle of these two lines due to
> patch4 allowing it and result in Paul's reported splat.
>
You might be right; at this point we would still have BALANCE_PUSH set,
so something like the below could happen
rebind_workers()
set_cpus_allowed_ptr()
affine_move_task()
task_running() => stop_one_cpu()
... // Stopper migrates the kworker here in the meantime
switch_to(<pcpu kworker>) // Both cpuhp thread and kworker should be enqueued
// here, so one or the other could be picked
balance_switch()
balance_push()
^-- no KTHREAD_IS_PER_CPU !
This should however trigger the WARN_ON_ONCE() in kthread_set_per_cpu()
*before* the one in process_one_work(), which I haven't seen in Paul's
mails.
>> + }
>>
>> raw_spin_lock_irq(&pool->lock);
>>
>>
>>
