[PATCH 5/8] workqueue: Tag bound workers with KTHREAD_IS_PER_CPU

[Peter Zijlstra]

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) <pet...@infradead.org>
---
 kernel/workqueue.c |   25 ++++++++++++++++++-------
 1 file changed, 18 insertions(+), 7 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, pool->cpu);
 
        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, -1);
        list_del(&worker->node);
        worker->pool = NULL;
 
@@ -2368,6 +2371,7 @@ static int worker_thread(void *__worker)
        /* tell the scheduler that this is a workqueue worker */
        set_pf_worker(true);
 woke_up:
+       kthread_parkme();
        raw_spin_lock_irq(&pool->lock);
 
        /* am I supposed to die? */
@@ -2425,7 +2429,7 @@ static int worker_thread(void *__worker)
                        move_linked_works(work, &worker->scheduled, NULL);
                        process_scheduled_works(worker);
                }
-       } while (keep_working(pool));
+       } while (keep_working(pool) && !kthread_should_park());
 
        worker_set_flags(worker, WORKER_PREP);
 sleep:
@@ -2437,9 +2441,12 @@ static int worker_thread(void *__worker)
         * event.
         */
        worker_enter_idle(worker);
-       __set_current_state(TASK_IDLE);
+       set_current_state(TASK_IDLE);
        raw_spin_unlock_irq(&pool->lock);
-       schedule();
+
+       if (!kthread_should_park())
+               schedule();
+
        goto woke_up;
 }
 
@@ -4919,8 +4926,10 @@ 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, -1);
                        WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task, 
cpu_possible_mask) < 0);
+               }
 
                mutex_unlock(&wq_pool_attach_mutex);
 
@@ -4972,9 +4981,11 @@ 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)
-               WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task,
-                                                 pool->attrs->cpumask) < 0);
+       for_each_pool_worker(worker, pool) {
+               WARN_ON_ONCE(kthread_park(worker->task) < 0);
+               kthread_set_per_cpu(worker->task, pool->cpu);
+               kthread_unpark(worker->task);
+       }
 
        raw_spin_lock_irq(&pool->lock);