2 files changed, 210 insertions, 71 deletions

diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index a0143dd24430..ac551b8ee7d9 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -335,6 +335,7 @@ enum {
 	 */
 	WQ_POWER_EFFICIENT	= 1 << 7,
 
+	__WQ_DESTROYING		= 1 << 15, /* internal: workqueue is destroying */
 	__WQ_DRAINING		= 1 << 16, /* internal: workqueue is draining */
 	__WQ_ORDERED		= 1 << 17, /* internal: workqueue is ordered */
 	__WQ_LEGACY		= 1 << 18, /* internal: create*_workqueue() */
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 07895deca271..b8b541caed48 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -169,7 +169,9 @@ struct worker_pool {
 
 	struct list_head	idle_list;	/* L: list of idle workers */
 	struct timer_list	idle_timer;	/* L: worker idle timeout */
-	struct timer_list	mayday_timer;	/* L: SOS timer for workers */
+	struct work_struct      idle_cull_work; /* L: worker idle cleanup */
+
+	struct timer_list	mayday_timer;	  /* L: SOS timer for workers */
 
 	/* a workers is either on busy_hash or idle_list, or the manager */
 	DECLARE_HASHTABLE(busy_hash, BUSY_WORKER_HASH_ORDER);
@@ -177,6 +179,7 @@ struct worker_pool {
 
 	struct worker		*manager;	/* L: purely informational */
 	struct list_head	workers;	/* A: attached workers */
+	struct list_head        dying_workers;  /* A: workers about to die */
 	struct completion	*detach_completion; /* all workers detached */
 
 	struct ida		worker_ida;	/* worker IDs for task name */
@@ -326,7 +329,7 @@ static struct rcuwait manager_wait = __RCUWAIT_INITIALIZER(manager_wait);
 static LIST_HEAD(workqueues);		/* PR: list of all workqueues */
 static bool workqueue_freezing;		/* PL: have wqs started freezing? */
 
-/* PL: allowable cpus for unbound wqs and work items */
+/* PL&A: allowable cpus for unbound wqs and work items */
 static cpumask_var_t wq_unbound_cpumask;
 
 /* CPU where unbound work was last round robin scheduled from this CPU */
@@ -1433,9 +1436,13 @@ static void __queue_work(int cpu, struct workqueue_struct *wq,
 	lockdep_assert_irqs_disabled();
 
 
-	/* if draining, only works from the same workqueue are allowed */
-	if (unlikely(wq->flags & __WQ_DRAINING) &&
-	    WARN_ON_ONCE(!is_chained_work(wq)))
+	/*
+	 * For a draining wq, only works from the same workqueue are
+	 * allowed. The __WQ_DESTROYING helps to spot the issue that
+	 * queues a new work item to a wq after destroy_workqueue(wq).
+	 */
+	if (unlikely(wq->flags & (__WQ_DESTROYING | __WQ_DRAINING) &&
+		     WARN_ON_ONCE(!is_chained_work(wq))))
 		return;
 	rcu_read_lock();
 retry:
@@ -1900,7 +1907,7 @@ static void worker_detach_from_pool(struct worker *worker)
 	list_del(&worker->node);
 	worker->pool = NULL;
 
-	if (list_empty(&pool->workers))
+	if (list_empty(&pool->workers) && list_empty(&pool->dying_workers))
 		detach_completion = pool->detach_completion;
 	mutex_unlock(&wq_pool_attach_mutex);
 
@@ -1972,21 +1979,55 @@ fail:
 	return NULL;
 }
 
+static void unbind_worker(struct worker *worker)
+{
+	lockdep_assert_held(&wq_pool_attach_mutex);
+
+	kthread_set_per_cpu(worker->task, -1);
+	if (cpumask_intersects(wq_unbound_cpumask, cpu_active_mask))
+		WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task, wq_unbound_cpumask) < 0);
+	else
+		WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task, cpu_possible_mask) < 0);
+}
+
+static void wake_dying_workers(struct list_head *cull_list)
+{
+	struct worker *worker, *tmp;
+
+	list_for_each_entry_safe(worker, tmp, cull_list, entry) {
+		list_del_init(&worker->entry);
+		unbind_worker(worker);
+		/*
+		 * If the worker was somehow already running, then it had to be
+		 * in pool->idle_list when set_worker_dying() happened or we
+		 * wouldn't have gotten here.
+		 *
+		 * Thus, the worker must either have observed the WORKER_DIE
+		 * flag, or have set its state to TASK_IDLE. Either way, the
+		 * below will be observed by the worker and is safe to do
+		 * outside of pool->lock.
+		 */
+		wake_up_process(worker->task);
+	}
+}
+
 /**
- * destroy_worker - destroy a workqueue worker
+ * set_worker_dying - Tag a worker for destruction
  * @worker: worker to be destroyed
+ * @list: transfer worker away from its pool->idle_list and into list
  *
- * Destroy @worker and adjust @pool stats accordingly.  The worker should
- * be idle.
+ * Tag @worker for destruction and adjust @pool stats accordingly.  The worker
+ * should be idle.
  *
  * CONTEXT:
  * raw_spin_lock_irq(pool->lock).
  */
-static void destroy_worker(struct worker *worker)
+static void set_worker_dying(struct worker *worker, struct list_head *list)
 {
 	struct worker_pool *pool = worker->pool;
 
 	lockdep_assert_held(&pool->lock);
+	lockdep_assert_held(&wq_pool_attach_mutex);
 
 	/* sanity check frenzy */
 	if (WARN_ON(worker->current_work) ||
@@ -1997,34 +2038,94 @@ static void destroy_worker(struct worker *worker)
 	pool->nr_workers--;
 	pool->nr_idle--;
 
-	list_del_init(&worker->entry);
 	worker->flags |= WORKER_DIE;
-	wake_up_process(worker->task);
+
+	list_move(&worker->entry, list);
+	list_move(&worker->node, &pool->dying_workers);
 }
 
+/**
+ * idle_worker_timeout - check if some idle workers can now be deleted.
+ * @t: The pool's idle_timer that just expired
+ *
+ * The timer is armed in worker_enter_idle(). Note that it isn't disarmed in
+ * worker_leave_idle(), as a worker flicking between idle and active while its
+ * pool is at the too_many_workers() tipping point would cause too much timer
+ * housekeeping overhead. Since IDLE_WORKER_TIMEOUT is long enough, we just let
+ * it expire and re-evaluate things from there.
+ */
 static void idle_worker_timeout(struct timer_list *t)
 {
 	struct worker_pool *pool = from_timer(pool, t, idle_timer);
+	bool do_cull = false;
+
+	if (work_pending(&pool->idle_cull_work))
+		return;
 
 	raw_spin_lock_irq(&pool->lock);
 
-	while (too_many_workers(pool)) {
+	if (too_many_workers(pool)) {
 		struct worker *worker;
 		unsigned long expires;
 
 		/* idle_list is kept in LIFO order, check the last one */
 		worker = list_entry(pool->idle_list.prev, struct worker, entry);
 		expires = worker->last_active + IDLE_WORKER_TIMEOUT;
+		do_cull = !time_before(jiffies, expires);
+
+		if (!do_cull)
+			mod_timer(&pool->idle_timer, expires);
+	}
+	raw_spin_unlock_irq(&pool->lock);
+
+	if (do_cull)
+		queue_work(system_unbound_wq, &pool->idle_cull_work);
+}
+
+/**
+ * idle_cull_fn - cull workers that have been idle for too long.
+ * @work: the pool's work for handling these idle workers
+ *
+ * This goes through a pool's idle workers and gets rid of those that have been
+ * idle for at least IDLE_WORKER_TIMEOUT seconds.
+ *
+ * We don't want to disturb isolated CPUs because of a pcpu kworker being
+ * culled, so this also resets worker affinity. This requires a sleepable
+ * context, hence the split between timer callback and work item.
+ */
+static void idle_cull_fn(struct work_struct *work)
+{
+	struct worker_pool *pool = container_of(work, struct worker_pool, idle_cull_work);
+	struct list_head cull_list;
+
+	INIT_LIST_HEAD(&cull_list);
+	/*
+	 * Grabbing wq_pool_attach_mutex here ensures an already-running worker
+	 * cannot proceed beyong worker_detach_from_pool() in its self-destruct
+	 * path. This is required as a previously-preempted worker could run after
+	 * set_worker_dying() has happened but before wake_dying_workers() did.
+	 */
+	mutex_lock(&wq_pool_attach_mutex);
+	raw_spin_lock_irq(&pool->lock);
+
+	while (too_many_workers(pool)) {
+		struct worker *worker;
+		unsigned long expires;
+
+		worker = list_entry(pool->idle_list.prev, struct worker, entry);
+		expires = worker->last_active + IDLE_WORKER_TIMEOUT;
 
 		if (time_before(jiffies, expires)) {
 			mod_timer(&pool->idle_timer, expires);
 			break;
 		}
 
-		destroy_worker(worker);
+		set_worker_dying(worker, &cull_list);
 	}
 
 	raw_spin_unlock_irq(&pool->lock);
+	wake_dying_workers(&cull_list);
+	mutex_unlock(&wq_pool_attach_mutex);
 }
 
 static void send_mayday(struct work_struct *work)
@@ -2388,12 +2489,12 @@ woke_up:
 	/* am I supposed to die? */
 	if (unlikely(worker->flags & WORKER_DIE)) {
 		raw_spin_unlock_irq(&pool->lock);
-		WARN_ON_ONCE(!list_empty(&worker->entry));
 		set_pf_worker(false);
 
 		set_task_comm(worker->task, "kworker/dying");
 		ida_free(&pool->worker_ida, worker->id);
 		worker_detach_from_pool(worker);
+		WARN_ON_ONCE(!list_empty(&worker->entry));
 		kfree(worker);
 		return 0;
 	}
@@ -3462,10 +3563,12 @@ static int init_worker_pool(struct worker_pool *pool)
 	hash_init(pool->busy_hash);
 
 	timer_setup(&pool->idle_timer, idle_worker_timeout, TIMER_DEFERRABLE);
+	INIT_WORK(&pool->idle_cull_work, idle_cull_fn);
 
 	timer_setup(&pool->mayday_timer, pool_mayday_timeout, 0);
 
 	INIT_LIST_HEAD(&pool->workers);
+	INIT_LIST_HEAD(&pool->dying_workers);
 
 	ida_init(&pool->worker_ida);
 	INIT_HLIST_NODE(&pool->hash_node);
@@ -3540,18 +3643,6 @@ static void rcu_free_pool(struct rcu_head *rcu)
 	kfree(pool);
 }
 
-/* This returns with the lock held on success (pool manager is inactive). */
-static bool wq_manager_inactive(struct worker_pool *pool)
-{
-	raw_spin_lock_irq(&pool->lock);
-
-	if (pool->flags & POOL_MANAGER_ACTIVE) {
-		raw_spin_unlock_irq(&pool->lock);
-		return false;
-	}
-	return true;
-}
-
 /**
  * put_unbound_pool - put a worker_pool
  * @pool: worker_pool to put
@@ -3566,8 +3657,11 @@ static bool wq_manager_inactive(struct worker_pool *pool)
 static void put_unbound_pool(struct worker_pool *pool)
 {
 	DECLARE_COMPLETION_ONSTACK(detach_completion);
+	struct list_head cull_list;
 	struct worker *worker;
 
+	INIT_LIST_HEAD(&cull_list);
+
 	lockdep_assert_held(&wq_pool_mutex);
 
 	if (--pool->refcnt)
@@ -3587,20 +3681,38 @@ static void put_unbound_pool(struct worker_pool *pool)
 	 * Become the manager and destroy all workers.  This prevents
 	 * @pool's workers from blocking on attach_mutex.  We're the last
 	 * manager and @pool gets freed with the flag set.
-	 * Because of how wq_manager_inactive() works, we will hold the
-	 * spinlock after a successful wait.
+	 *
+	 * Having a concurrent manager is quite unlikely to happen as we can
+	 * only get here with
+	 *   pwq->refcnt == pool->refcnt == 0
+	 * which implies no work queued to the pool, which implies no worker can
+	 * become the manager. However a worker could have taken the role of
+	 * manager before the refcnts dropped to 0, since maybe_create_worker()
+	 * drops pool->lock
 	 */
-	rcuwait_wait_event(&manager_wait, wq_manager_inactive(pool),
-			   TASK_UNINTERRUPTIBLE);
-	pool->flags |= POOL_MANAGER_ACTIVE;
+	while (true) {
+		rcuwait_wait_event(&manager_wait,
+				   !(pool->flags & POOL_MANAGER_ACTIVE),
+				   TASK_UNINTERRUPTIBLE);
+
+		mutex_lock(&wq_pool_attach_mutex);
+		raw_spin_lock_irq(&pool->lock);
+		if (!(pool->flags & POOL_MANAGER_ACTIVE)) {
+			pool->flags |= POOL_MANAGER_ACTIVE;
+			break;
+		}
+		raw_spin_unlock_irq(&pool->lock);
+		mutex_unlock(&wq_pool_attach_mutex);
+	}
 
 	while ((worker = first_idle_worker(pool)))
-		destroy_worker(worker);
+		set_worker_dying(worker, &cull_list);
 	WARN_ON(pool->nr_workers || pool->nr_idle);
 	raw_spin_unlock_irq(&pool->lock);
 
-	mutex_lock(&wq_pool_attach_mutex);
-	if (!list_empty(&pool->workers))
+	wake_dying_workers(&cull_list);
+
+	if (!list_empty(&pool->workers) || !list_empty(&pool->dying_workers))
 		pool->detach_completion = &detach_completion;
 	mutex_unlock(&wq_pool_attach_mutex);
 
@@ -3609,6 +3721,7 @@ static void put_unbound_pool(struct worker_pool *pool)
 
 	/* shut down the timers */
 	del_timer_sync(&pool->idle_timer);
+	cancel_work_sync(&pool->idle_cull_work);
 	del_timer_sync(&pool->mayday_timer);
 
 	/* RCU protected to allow dereferences from get_work_pool() */
@@ -3952,7 +4065,8 @@ static void apply_wqattrs_cleanup(struct apply_wqattrs_ctx *ctx)
 /* allocate the attrs and pwqs for later installation */
 static struct apply_wqattrs_ctx *
 apply_wqattrs_prepare(struct workqueue_struct *wq,
-		      const struct workqueue_attrs *attrs)
+		      const struct workqueue_attrs *attrs,
+		      const cpumask_var_t unbound_cpumask)
 {
 	struct apply_wqattrs_ctx *ctx;
 	struct workqueue_attrs *new_attrs, *tmp_attrs;
@@ -3968,14 +4082,15 @@ apply_wqattrs_prepare(struct workqueue_struct *wq,
 		goto out_free;
 
 	/*
-	 * Calculate the attrs of the default pwq.
+	 * Calculate the attrs of the default pwq with unbound_cpumask
+	 * which is wq_unbound_cpumask or to set to wq_unbound_cpumask.
 	 * If the user configured cpumask doesn't overlap with the
 	 * wq_unbound_cpumask, we fallback to the wq_unbound_cpumask.
 	 */
 	copy_workqueue_attrs(new_attrs, attrs);
-	cpumask_and(new_attrs->cpumask, new_attrs->cpumask, wq_unbound_cpumask);
+	cpumask_and(new_attrs->cpumask, new_attrs->cpumask, unbound_cpumask);
 	if (unlikely(cpumask_empty(new_attrs->cpumask)))
-		cpumask_copy(new_attrs->cpumask, wq_unbound_cpumask);
+		cpumask_copy(new_attrs->cpumask, unbound_cpumask);
 
 	/*
 	 * We may create multiple pwqs with differing cpumasks.  Make a
@@ -4072,7 +4187,7 @@ static int apply_workqueue_attrs_locked(struct workqueue_struct *wq,
 		wq->flags &= ~__WQ_ORDERED;
 	}
 
-	ctx = apply_wqattrs_prepare(wq, attrs);
+	ctx = apply_wqattrs_prepare(wq, attrs, wq_unbound_cpumask);
 	if (!ctx)
 		return -ENOMEM;
 
@@ -4414,6 +4529,11 @@ void destroy_workqueue(struct workqueue_struct *wq)
 	 */
 	workqueue_sysfs_unregister(wq);
 
+	/* mark the workqueue destruction is in progress */
+	mutex_lock(&wq->mutex);
+	wq->flags |= __WQ_DESTROYING;
+	mutex_unlock(&wq->mutex);
+
 	/* drain it before proceeding with destruction */
 	drain_workqueue(wq);
 
@@ -4709,22 +4829,53 @@ static void pr_cont_pool_info(struct worker_pool *pool)
 	pr_cont(" flags=0x%x nice=%d", pool->flags, pool->attrs->nice);
 }
 
-static void pr_cont_work(bool comma, struct work_struct *work)
+struct pr_cont_work_struct {
+	bool comma;
+	work_func_t func;
+	long ctr;
+};
+
+static void pr_cont_work_flush(bool comma, work_func_t func, struct pr_cont_work_struct *pcwsp)
+{
+	if (!pcwsp->ctr)
+		goto out_record;
+	if (func == pcwsp->func) {
+		pcwsp->ctr++;
+		return;
+	}
+	if (pcwsp->ctr == 1)
+		pr_cont("%s %ps", pcwsp->comma ? "," : "", pcwsp->func);
+	else
+		pr_cont("%s %ld*%ps", pcwsp->comma ? "," : "", pcwsp->ctr, pcwsp->func);
+	pcwsp->ctr = 0;
+out_record:
+	if ((long)func == -1L)
+		return;
+	pcwsp->comma = comma;
+	pcwsp->func = func;
+	pcwsp->ctr = 1;
+}
+
+static void pr_cont_work(bool comma, struct work_struct *work, struct pr_cont_work_struct *pcwsp)
 {
 	if (work->func == wq_barrier_func) {
 		struct wq_barrier *barr;
 
 		barr = container_of(work, struct wq_barrier, work);
 
+		pr_cont_work_flush(comma, (work_func_t)-1, pcwsp);
 		pr_cont("%s BAR(%d)", comma ? "," : "",
 			task_pid_nr(barr->task));
 	} else {
-		pr_cont("%s %ps", comma ? "," : "", work->func);
+		if (!comma)
+			pr_cont_work_flush(comma, (work_func_t)-1, pcwsp);
+		pr_cont_work_flush(comma, work->func, pcwsp);
 	}
 }
 
 static void show_pwq(struct pool_workqueue *pwq)
 {
+	struct pr_cont_work_struct pcws = { .ctr = 0, };
 	struct worker_pool *pool = pwq->pool;
 	struct work_struct *work;
 	struct worker *worker;
@@ -4757,7 +4908,8 @@ static void show_pwq(struct pool_workqueue *pwq)
 				worker->rescue_wq ? "(RESCUER)" : "",
 				worker->current_func);
 			list_for_each_entry(work, &worker->scheduled, entry)
-				pr_cont_work(false, work);
+				pr_cont_work(false, work, &pcws);
+			pr_cont_work_flush(comma, (work_func_t)-1L, &pcws);
 			comma = true;
 		}
 		pr_cont("\n");
@@ -4777,9 +4929,10 @@ static void show_pwq(struct pool_workqueue *pwq)
 			if (get_work_pwq(work) != pwq)
 				continue;
 
-			pr_cont_work(comma, work);
+			pr_cont_work(comma, work, &pcws);
 			comma = !(*work_data_bits(work) & WORK_STRUCT_LINKED);
 		}
+		pr_cont_work_flush(comma, (work_func_t)-1L, &pcws);
 		pr_cont("\n");
 	}
 
@@ -4788,9 +4941,10 @@ static void show_pwq(struct pool_workqueue *pwq)
 
 		pr_info("    inactive:");
 		list_for_each_entry(work, &pwq->inactive_works, entry) {
-			pr_cont_work(comma, work);
+			pr_cont_work(comma, work, &pcws);
 			comma = !(*work_data_bits(work) & WORK_STRUCT_LINKED);
 		}
+		pr_cont_work_flush(comma, (work_func_t)-1L, &pcws);
 		pr_cont("\n");
 	}
 }
@@ -5006,13 +5160,8 @@ static void unbind_workers(int cpu)
 
 		raw_spin_unlock_irq(&pool->lock);
 
-		for_each_pool_worker(worker, pool) {
-			kthread_set_per_cpu(worker->task, -1);
-			if (cpumask_intersects(wq_unbound_cpumask, cpu_active_mask))
-				WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task, wq_unbound_cpumask) < 0);
-			else
-				WARN_ON_ONCE(set_cpus_allowed_ptr(worker->task, cpu_possible_mask) < 0);
-		}
+		for_each_pool_worker(worker, pool)
+			unbind_worker(worker);
 
 		mutex_unlock(&wq_pool_attach_mutex);
 	}
@@ -5334,7 +5483,7 @@ out_unlock:
 }
 #endif /* CONFIG_FREEZER */
 
-static int workqueue_apply_unbound_cpumask(void)
+static int workqueue_apply_unbound_cpumask(const cpumask_var_t unbound_cpumask)
 {
 	LIST_HEAD(ctxs);
 	int ret = 0;
@@ -5350,7 +5499,7 @@ static int workqueue_apply_unbound_cpumask(void)
 		if (wq->flags & __WQ_ORDERED)
 			continue;
 
-		ctx = apply_wqattrs_prepare(wq, wq->unbound_attrs);
+		ctx = apply_wqattrs_prepare(wq, wq->unbound_attrs, unbound_cpumask);
 		if (!ctx) {
 			ret = -ENOMEM;
 			break;
@@ -5365,6 +5514,11 @@ static int workqueue_apply_unbound_cpumask(void)
 		apply_wqattrs_cleanup(ctx);
 	}
 
+	if (!ret) {
+		mutex_lock(&wq_pool_attach_mutex);
+		cpumask_copy(wq_unbound_cpumask, unbound_cpumask);
+		mutex_unlock(&wq_pool_attach_mutex);
+	}
 	return ret;
 }
 
@@ -5383,7 +5537,6 @@ static int workqueue_apply_unbound_cpumask(void)
 int workqueue_set_unbound_cpumask(cpumask_var_t cpumask)
 {
 	int ret = -EINVAL;
-	cpumask_var_t saved_cpumask;
 
 	/*
 	 * Not excluding isolated cpus on purpose.
@@ -5397,23 +5550,8 @@ int workqueue_set_unbound_cpumask(cpumask_var_t cpumask)
 			goto out_unlock;
 		}
 
-		if (!zalloc_cpumask_var(&saved_cpumask, GFP_KERNEL)) {
-			ret = -ENOMEM;
-			goto out_unlock;
-		}
-
-		/* save the old wq_unbound_cpumask. */
-		cpumask_copy(saved_cpumask, wq_unbound_cpumask);
-
-		/* update wq_unbound_cpumask at first and apply it to wqs. */
-		cpumask_copy(wq_unbound_cpumask, cpumask);
-		ret = workqueue_apply_unbound_cpumask();
-
-		/* restore the wq_unbound_cpumask when failed. */
-		if (ret < 0)
-			cpumask_copy(wq_unbound_cpumask, saved_cpumask);
+		ret = workqueue_apply_unbound_cpumask(cpumask);
 
-		free_cpumask_var(saved_cpumask);
 out_unlock:
 		apply_wqattrs_unlock();
 	}