On Tue, Jan 12, 2021 at 10:51 PM Peter Zijlstra <[email protected]> wrote: > > Mark the per-cpu workqueue workers as KTHREAD_IS_PER_CPU. > > Workqueues have unfortunate semantics in that per-cpu workers are not > default flushed and parked during hotplug, however a subset does > manual flush on hotplug and hard relies on them for correctness. > > Therefore play silly games.. > > Signed-off-by: Peter Zijlstra (Intel) <[email protected]> > Tested-by: Paul E. McKenney <[email protected]> > --- > kernel/workqueue.c | 11 +++++++++-- > 1 file changed, 9 insertions(+), 2 deletions(-) > > --- a/kernel/workqueue.c > +++ b/kernel/workqueue.c > @@ -1861,6 +1861,8 @@ static void worker_attach_to_pool(struct > */ > if (pool->flags & POOL_DISASSOCIATED) > worker->flags |= WORKER_UNBOUND; > + else > + kthread_set_per_cpu(worker->task, true); > > list_add_tail(&worker->node, &pool->workers); > worker->pool = pool; > @@ -1883,6 +1885,7 @@ static void worker_detach_from_pool(stru > > mutex_lock(&wq_pool_attach_mutex); > > + kthread_set_per_cpu(worker->task, false); > list_del(&worker->node); > worker->pool = NULL; > > @@ -4919,8 +4922,10 @@ static void unbind_workers(int cpu) > > raw_spin_unlock_irq(&pool->lock); > > - for_each_pool_worker(worker, pool) > + for_each_pool_worker(worker, pool) { > + kthread_set_per_cpu(worker->task, false); > WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task, > cpu_possible_mask) < 0); > + } > > mutex_unlock(&wq_pool_attach_mutex); > > @@ -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. > + } > > raw_spin_lock_irq(&pool->lock); > > >
