---

yaml
---
r: 316721
b: refs/heads/master
c: 25511a4
h: refs/heads/master
i:
  316719: 831af94
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: bc2ae0f5bb2f39e6db06a62f9d353e4601a332a1
+refs/heads/master: 25511a477657884d2164f338341fa89652610507

trunk/kernel/workqueue.c

@@ -133,6 +133,7 @@ enum {
 
 struct global_cwq;
 struct worker_pool;
+struct idle_rebind;
 
 /*
  * The poor guys doing the actual heavy lifting.  All on-duty workers
@@ -154,7 +155,10 @@ struct worker {
 	unsigned long		last_active;	/* L: last active timestamp */
 	unsigned int		flags;		/* X: flags */
 	int			id;		/* I: worker id */
-	struct work_struct	rebind_work;	/* L: rebind worker to cpu */
+
+	/* for rebinding worker to CPU */
+	struct idle_rebind	*idle_rebind;	/* L: for idle worker */
+	struct work_struct	rebind_work;	/* L: for busy worker */
 };
 
 struct worker_pool {
@@ -190,6 +194,8 @@ struct global_cwq {
 
 	struct worker_pool	pools[2];	/* normal and highpri pools */
 
+	wait_queue_head_t	rebind_hold;	/* rebind hold wait */
+
 	struct task_struct	*trustee;	/* L: for gcwq shutdown */
 	unsigned int		trustee_state;	/* L: trustee state */
 	wait_queue_head_t	trustee_wait;	/* trustee wait */
@@ -1314,13 +1320,37 @@ __acquires(&gcwq->lock)
 	}
 }
 
+struct idle_rebind {
+	int			cnt;		/* # workers to be rebound */
+	struct completion	done;		/* all workers rebound */
+};
+
+/*
+ * Rebind an idle @worker to its CPU.  During CPU onlining, this has to
+ * happen synchronously for idle workers.  worker_thread() will test
+ * %WORKER_REBIND before leaving idle and call this function.
+ */
+static void idle_worker_rebind(struct worker *worker)
+{
+	struct global_cwq *gcwq = worker->pool->gcwq;
+
+	/* CPU must be online at this point */
+	WARN_ON(!worker_maybe_bind_and_lock(worker));
+	if (!--worker->idle_rebind->cnt)
+		complete(&worker->idle_rebind->done);
+	spin_unlock_irq(&worker->pool->gcwq->lock);
+
+	/* we did our part, wait for rebind_workers() to finish up */
+	wait_event(gcwq->rebind_hold, !(worker->flags & WORKER_REBIND));
+}
+
 /*
- * Function for worker->rebind_work used to rebind unbound busy workers to
+ * Function for @worker->rebind.work used to rebind unbound busy workers to
  * the associated cpu which is coming back online.  This is scheduled by
  * cpu up but can race with other cpu hotplug operations and may be
  * executed twice without intervening cpu down.
  */
-static void worker_rebind_fn(struct work_struct *work)
+static void busy_worker_rebind_fn(struct work_struct *work)
 {
 	struct worker *worker = container_of(work, struct worker, rebind_work);
 	struct global_cwq *gcwq = worker->pool->gcwq;
@@ -1331,6 +1361,112 @@ static void worker_rebind_fn(struct work_struct *work)
 	spin_unlock_irq(&gcwq->lock);
 }
 
+/**
+ * rebind_workers - rebind all workers of a gcwq to the associated CPU
+ * @gcwq: gcwq of interest
+ *
+ * @gcwq->cpu is coming online.  Rebind all workers to the CPU.  Rebinding
+ * is different for idle and busy ones.
+ *
+ * The idle ones should be rebound synchronously and idle rebinding should
+ * be complete before any worker starts executing work items with
+ * concurrency management enabled; otherwise, scheduler may oops trying to
+ * wake up non-local idle worker from wq_worker_sleeping().
+ *
+ * This is achieved by repeatedly requesting rebinding until all idle
+ * workers are known to have been rebound under @gcwq->lock and holding all
+ * idle workers from becoming busy until idle rebinding is complete.
+ *
+ * Once idle workers are rebound, busy workers can be rebound as they
+ * finish executing their current work items.  Queueing the rebind work at
+ * the head of their scheduled lists is enough.  Note that nr_running will
+ * be properbly bumped as busy workers rebind.
+ *
+ * On return, all workers are guaranteed to either be bound or have rebind
+ * work item scheduled.
+ */
+static void rebind_workers(struct global_cwq *gcwq)
+	__releases(&gcwq->lock) __acquires(&gcwq->lock)
+{
+	struct idle_rebind idle_rebind;
+	struct worker_pool *pool;
+	struct worker *worker;
+	struct hlist_node *pos;
+	int i;
+
+	lockdep_assert_held(&gcwq->lock);
+
+	for_each_worker_pool(pool, gcwq)
+		lockdep_assert_held(&pool->manager_mutex);
+
+	/*
+	 * Rebind idle workers.  Interlocked both ways.  We wait for
+	 * workers to rebind via @idle_rebind.done.  Workers will wait for
+	 * us to finish up by watching %WORKER_REBIND.
+	 */
+	init_completion(&idle_rebind.done);
+retry:
+	idle_rebind.cnt = 1;
+	INIT_COMPLETION(idle_rebind.done);
+
+	/* set REBIND and kick idle ones, we'll wait for these later */
+	for_each_worker_pool(pool, gcwq) {
+		list_for_each_entry(worker, &pool->idle_list, entry) {
+			if (worker->flags & WORKER_REBIND)
+				continue;
+
+			/* morph UNBOUND to REBIND */
+			worker->flags &= ~WORKER_UNBOUND;
+			worker->flags |= WORKER_REBIND;
+
+			idle_rebind.cnt++;
+			worker->idle_rebind = &idle_rebind;
+
+			/* worker_thread() will call idle_worker_rebind() */
+			wake_up_process(worker->task);
+		}
+	}
+
+	if (--idle_rebind.cnt) {
+		spin_unlock_irq(&gcwq->lock);
+		wait_for_completion(&idle_rebind.done);
+		spin_lock_irq(&gcwq->lock);
+		/* busy ones might have become idle while waiting, retry */
+		goto retry;
+	}
+
+	/*
+	 * All idle workers are rebound and waiting for %WORKER_REBIND to
+	 * be cleared inside idle_worker_rebind().  Clear and release.
+	 * Clearing %WORKER_REBIND from this foreign context is safe
+	 * because these workers are still guaranteed to be idle.
+	 */
+	for_each_worker_pool(pool, gcwq)
+		list_for_each_entry(worker, &pool->idle_list, entry)
+			worker->flags &= ~WORKER_REBIND;
+
+	wake_up_all(&gcwq->rebind_hold);
+
+	/* rebind busy workers */
+	for_each_busy_worker(worker, i, pos, gcwq) {
+		struct work_struct *rebind_work = &worker->rebind_work;
+
+		/* morph UNBOUND to REBIND */
+		worker->flags &= ~WORKER_UNBOUND;
+		worker->flags |= WORKER_REBIND;
+
+		if (test_and_set_bit(WORK_STRUCT_PENDING_BIT,
+				     work_data_bits(rebind_work)))
+			continue;
+
+		/* wq doesn't matter, use the default one */
+		debug_work_activate(rebind_work);
+		insert_work(get_cwq(gcwq->cpu, system_wq), rebind_work,
+			    worker->scheduled.next,
+			    work_color_to_flags(WORK_NO_COLOR));
+	}
+}
+
 static struct worker *alloc_worker(void)
 {
 	struct worker *worker;
@@ -1339,7 +1475,7 @@ static struct worker *alloc_worker(void)
 	if (worker) {
 		INIT_LIST_HEAD(&worker->entry);
 		INIT_LIST_HEAD(&worker->scheduled);
-		INIT_WORK(&worker->rebind_work, worker_rebind_fn);
+		INIT_WORK(&worker->rebind_work, busy_worker_rebind_fn);
 		/* on creation a worker is in !idle && prep state */
 		worker->flags = WORKER_PREP;
 	}
@@ -1829,6 +1965,9 @@ __acquires(&gcwq->lock)
 
 	lockdep_copy_map(&lockdep_map, &work->lockdep_map);
 #endif
+	WARN_ON_ONCE(!(worker->flags & (WORKER_UNBOUND | WORKER_REBIND)) &&
+		     raw_smp_processor_id() != gcwq->cpu);
+
 	/*
 	 * A single work shouldn't be executed concurrently by
 	 * multiple workers on a single cpu.  Check whether anyone is
@@ -1946,11 +2085,20 @@ static int worker_thread(void *__worker)
 woke_up:
 	spin_lock_irq(&gcwq->lock);
 
-	/* DIE can be set only while we're idle, checking here is enough */
-	if (worker->flags & WORKER_DIE) {
+	/*
+	 * DIE can be set only while idle and REBIND set while busy has
+	 * @worker->rebind_work scheduled.  Checking here is enough.
+	 */
+	if (unlikely(worker->flags & (WORKER_REBIND | WORKER_DIE))) {
 		spin_unlock_irq(&gcwq->lock);
-		worker->task->flags &= ~PF_WQ_WORKER;
-		return 0;
+
+		if (worker->flags & WORKER_DIE) {
+			worker->task->flags &= ~PF_WQ_WORKER;
+			return 0;
+		}
+
+		idle_worker_rebind(worker);
+		goto woke_up;
 	}
 
 	worker_leave_idle(worker);
@@ -3468,42 +3616,6 @@ static int __cpuinit trustee_thread(void *__gcwq)
 		}
 	} while (i && rc >= 0);
 
-	/*
-	 * At this point, either draining has completed and no worker
-	 * is left, or cpu down has been canceled or the cpu is being
-	 * brought back up.  There shouldn't be any idle one left.
-	 * Tell the remaining busy ones to rebind once it finishes the
-	 * currently scheduled works by scheduling the rebind_work.
-	 */
-	for_each_worker_pool(pool, gcwq)
-		WARN_ON(!list_empty(&pool->idle_list));
-
-	/* if we're reassociating, clear DISASSOCIATED */
-	if (gcwq->trustee_state == TRUSTEE_RELEASE)
-		gcwq->flags &= ~GCWQ_DISASSOCIATED;
-
-	for_each_busy_worker(worker, i, pos, gcwq) {
-		struct work_struct *rebind_work = &worker->rebind_work;
-
-		/*
-		 * Rebind_work may race with future cpu hotplug
-		 * operations.  Use a separate flag to mark that
-		 * rebinding is scheduled.
-		 */
-		worker->flags |= WORKER_REBIND;
-		worker->flags &= ~WORKER_UNBOUND;
-
-		/* queue rebind_work, wq doesn't matter, use the default one */
-		if (test_and_set_bit(WORK_STRUCT_PENDING_BIT,
-				     work_data_bits(rebind_work)))
-			continue;
-
-		debug_work_activate(rebind_work);
-		insert_work(get_cwq(gcwq->cpu, system_wq), rebind_work,
-			    worker->scheduled.next,
-			    work_color_to_flags(WORK_NO_COLOR));
-	}
-
 	gcwq_release_management(gcwq);
 
 	/* notify completion */
@@ -3609,13 +3721,16 @@ static int __devinit workqueue_cpu_callback(struct notifier_block *nfb,
 			wait_trustee_state(gcwq, TRUSTEE_DONE);
 		}
 
-		/*
-		 * Either DISASSOCIATED is already cleared or no worker is
-		 * left on the gcwq.  Safe to clear DISASSOCIATED without
-		 * claiming managers.
-		 */
+		spin_unlock_irq(&gcwq->lock);
+		gcwq_claim_management(gcwq);
+		spin_lock_irq(&gcwq->lock);
+
 		gcwq->flags &= ~GCWQ_DISASSOCIATED;
 
+		rebind_workers(gcwq);
+
+		gcwq_release_management(gcwq);
+
 		/*
 		 * Trustee is done and there might be no worker left.
 		 * Put the first_idle in and request a real manager to
@@ -3910,6 +4025,8 @@ static int __init init_workqueues(void)
 			ida_init(&pool->worker_ida);
 		}
 
+		init_waitqueue_head(&gcwq->rebind_hold);
+
 		gcwq->trustee_state = TRUSTEE_DONE;
 		init_waitqueue_head(&gcwq->trustee_wait);
 	}