* attach_mutex to avoid changing binding state while
* worker_attach_to_pool() is in progress.
*/
+ POOL_MANAGER_ACTIVE = 1 << 0, /* being managed */
POOL_DISASSOCIATED = 1 << 2, /* cpu can't serve workers */
/* worker flags */
/* L: hash of busy workers */
/* see manage_workers() for details on the two manager mutexes */
- struct mutex manager_arb; /* manager arbitration */
struct worker *manager; /* L: purely informational */
struct mutex attach_mutex; /* attach/detach exclusion */
struct list_head workers; /* A: attached workers */
static DEFINE_MUTEX(wq_pool_mutex); /* protects pools and workqueues list */
static DEFINE_SPINLOCK(wq_mayday_lock); /* protects wq->maydays list */
+static DECLARE_WAIT_QUEUE_HEAD(wq_manager_wait); /* wait for manager to go away */
static LIST_HEAD(workqueues); /* PR: list of all workqueues */
static bool workqueue_freezing; /* PL: have wqs started freezing? */
int node)
{
assert_rcu_or_wq_mutex_or_pool_mutex(wq);
+
+ /*
+ * XXX: @node can be NUMA_NO_NODE if CPU goes offline while a
+ * delayed item is pending. The plan is to keep CPU -> NODE
+ * mapping valid and stable across CPU on/offlines. Once that
+ * happens, this workaround can be removed.
+ */
+ if (unlikely(node == NUMA_NO_NODE))
+ return wq->dfl_pwq;
+
return rcu_dereference_raw(wq->numa_pwq_tbl[node]);
}
*/
smp_wmb();
set_work_data(work, (unsigned long)pool_id << WORK_OFFQ_POOL_SHIFT, 0);
+ /*
+ * The following mb guarantees that previous clear of a PENDING bit
+ * will not be reordered with any speculative LOADS or STORES from
+ * work->current_func, which is executed afterwards. This possible
+ * reordering can lead to a missed execution on attempt to qeueue
+ * the same @work. E.g. consider this case:
+ *
+ * CPU#0 CPU#1
+ * ---------------------------- --------------------------------
+ *
+ * 1 STORE event_indicated
+ * 2 queue_work_on() {
+ * 3 test_and_set_bit(PENDING)
+ * 4 } set_..._and_clear_pending() {
+ * 5 set_work_data() # clear bit
+ * 6 smp_mb()
+ * 7 work->current_func() {
+ * 8 LOAD event_indicated
+ * }
+ *
+ * Without an explicit full barrier speculative LOAD on line 8 can
+ * be executed before CPU#0 does STORE on line 1. If that happens,
+ * CPU#0 observes the PENDING bit is still set and new execution of
+ * a @work is not queued in a hope, that CPU#1 will eventually
+ * finish the queued @work. Meanwhile CPU#1 does not see
+ * event_indicated is set, because speculative LOAD was executed
+ * before actual STORE.
+ */
+ smp_mb();
}
static void clear_work_data(struct work_struct *work)
/* Do we have too many workers and should some go away? */
static bool too_many_workers(struct worker_pool *pool)
{
- bool managing = mutex_is_locked(&pool->manager_arb);
+ bool managing = pool->flags & POOL_MANAGER_ACTIVE;
int nr_idle = pool->nr_idle + managing; /* manager is considered idle */
int nr_busy = pool->nr_workers - nr_idle;
struct timer_list *timer = &dwork->timer;
struct work_struct *work = &dwork->work;
+ WARN_ON_ONCE(!wq);
WARN_ON_ONCE(timer->function != delayed_work_timer_fn ||
timer->data != (unsigned long)dwork);
WARN_ON_ONCE(timer_pending(timer));
timer_stats_timer_set_start_info(&dwork->timer);
dwork->wq = wq;
- /* timer isn't guaranteed to run in this cpu, record earlier */
- if (cpu == WORK_CPU_UNBOUND)
- cpu = raw_smp_processor_id();
dwork->cpu = cpu;
timer->expires = jiffies + delay;
- add_timer_on(timer, cpu);
+ if (unlikely(cpu != WORK_CPU_UNBOUND))
+ add_timer_on(timer, cpu);
+ else
+ add_timer(timer);
}
/**
{
struct worker_pool *pool = worker->pool;
- /*
- * Anyone who successfully grabs manager_arb wins the arbitration
- * and becomes the manager. mutex_trylock() on pool->manager_arb
- * failure while holding pool->lock reliably indicates that someone
- * else is managing the pool and the worker which failed trylock
- * can proceed to executing work items. This means that anyone
- * grabbing manager_arb is responsible for actually performing
- * manager duties. If manager_arb is grabbed and released without
- * actual management, the pool may stall indefinitely.
- */
- if (!mutex_trylock(&pool->manager_arb))
+ if (pool->flags & POOL_MANAGER_ACTIVE)
return false;
+
+ pool->flags |= POOL_MANAGER_ACTIVE;
pool->manager = worker;
maybe_create_worker(pool);
pool->manager = NULL;
- mutex_unlock(&pool->manager_arb);
+ pool->flags &= ~POOL_MANAGER_ACTIVE;
+ wake_up(&wq_manager_wait);
return true;
}
*/
if (need_to_create_worker(pool)) {
spin_lock(&wq_mayday_lock);
- get_pwq(pwq);
- list_move_tail(&pwq->mayday_node, &wq->maydays);
+ /*
+ * Queue iff we aren't racing destruction
+ * and somebody else hasn't queued it already.
+ */
+ if (wq->rescuer && list_empty(&pwq->mayday_node)) {
+ get_pwq(pwq);
+ list_add_tail(&pwq->mayday_node, &wq->maydays);
+ }
spin_unlock(&wq_mayday_lock);
}
}
setup_timer(&pool->mayday_timer, pool_mayday_timeout,
(unsigned long)pool);
- mutex_init(&pool->manager_arb);
mutex_init(&pool->attach_mutex);
INIT_LIST_HEAD(&pool->workers);
hash_del(&pool->hash_node);
/*
- * Become the manager and destroy all workers. Grabbing
- * manager_arb prevents @pool's workers from blocking on
- * attach_mutex.
+ * 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.
*/
- mutex_lock(&pool->manager_arb);
-
spin_lock_irq(&pool->lock);
+ wait_event_lock_irq(wq_manager_wait,
+ !(pool->flags & POOL_MANAGER_ACTIVE), pool->lock);
+ pool->flags |= POOL_MANAGER_ACTIVE;
+
while ((worker = first_idle_worker(pool)))
destroy_worker(worker);
WARN_ON(pool->nr_workers || pool->nr_idle);
if (pool->detach_completion)
wait_for_completion(pool->detach_completion);
- mutex_unlock(&pool->manager_arb);
-
/* shut down the timers */
del_timer_sync(&pool->idle_timer);
del_timer_sync(&pool->mayday_timer);
return -EINVAL;
/* creating multiple pwqs breaks ordering guarantee */
- if (WARN_ON((wq->flags & __WQ_ORDERED) && !list_empty(&wq->pwqs)))
- return -EINVAL;
+ if (!list_empty(&wq->pwqs)) {
+ if (WARN_ON(wq->flags & __WQ_ORDERED_EXPLICIT))
+ return -EINVAL;
+
+ wq->flags &= ~__WQ_ORDERED;
+ }
ctx = apply_wqattrs_prepare(wq, attrs);
struct workqueue_struct *wq;
struct pool_workqueue *pwq;
+ /*
+ * Unbound && max_active == 1 used to imply ordered, which is no
+ * longer the case on NUMA machines due to per-node pools. While
+ * alloc_ordered_workqueue() is the right way to create an ordered
+ * workqueue, keep the previous behavior to avoid subtle breakages
+ * on NUMA.
+ */
+ if ((flags & WQ_UNBOUND) && max_active == 1)
+ flags |= __WQ_ORDERED;
+
/* see the comment above the definition of WQ_POWER_EFFICIENT */
if ((flags & WQ_POWER_EFFICIENT) && wq_power_efficient)
flags |= WQ_UNBOUND;
struct pool_workqueue *pwq;
int node;
+ /*
+ * Remove it from sysfs first so that sanity check failure doesn't
+ * lead to sysfs name conflicts.
+ */
+ workqueue_sysfs_unregister(wq);
+
/* drain it before proceeding with destruction */
drain_workqueue(wq);
+ /* kill rescuer, if sanity checks fail, leave it w/o rescuer */
+ if (wq->rescuer) {
+ struct worker *rescuer = wq->rescuer;
+
+ /* this prevents new queueing */
+ spin_lock_irq(&wq_mayday_lock);
+ wq->rescuer = NULL;
+ spin_unlock_irq(&wq_mayday_lock);
+
+ /* rescuer will empty maydays list before exiting */
+ kthread_stop(rescuer->task);
+ kfree(rescuer);
+ }
+
/* sanity checks */
mutex_lock(&wq->mutex);
for_each_pwq(pwq, wq) {
list_del_rcu(&wq->list);
mutex_unlock(&wq_pool_mutex);
- workqueue_sysfs_unregister(wq);
-
- if (wq->rescuer)
- kthread_stop(wq->rescuer->task);
-
if (!(wq->flags & WQ_UNBOUND)) {
/*
* The base ref is never dropped on per-cpu pwqs. Directly
struct pool_workqueue *pwq;
/* disallow meddling with max_active for ordered workqueues */
- if (WARN_ON(wq->flags & __WQ_ORDERED))
+ if (WARN_ON(wq->flags & __WQ_ORDERED_EXPLICIT))
return;
max_active = wq_clamp_max_active(max_active, wq->flags, wq->name);
mutex_lock(&wq->mutex);
+ wq->flags &= ~__WQ_ORDERED;
wq->saved_max_active = max_active;
for_each_pwq(pwq, wq)
EXPORT_SYMBOL_GPL(workqueue_set_max_active);
/**
+ * current_work - retrieve %current task's work struct
+ *
+ * Determine if %current task is a workqueue worker and what it's working on.
+ * Useful to find out the context that the %current task is running in.
+ *
+ * Return: work struct if %current task is a workqueue worker, %NULL otherwise.
+ */
+struct work_struct *current_work(void)
+{
+ struct worker *worker = current_wq_worker();
+
+ return worker ? worker->current_work : NULL;
+}
+EXPORT_SYMBOL(current_work);
+
+/**
* current_is_workqueue_rescuer - is %current workqueue rescuer?
*
* Determine whether %current is a workqueue rescuer. Can be used from
pr_info(" pwq %d:", pool->id);
pr_cont_pool_info(pool);
- pr_cont(" active=%d/%d%s\n", pwq->nr_active, pwq->max_active,
+ pr_cont(" active=%d/%d refcnt=%d%s\n",
+ pwq->nr_active, pwq->max_active, pwq->refcnt,
!list_empty(&pwq->mayday_node) ? " MAYDAY" : "");
hash_for_each(pool->busy_hash, bkt, worker, hentry) {
pool->attrs->cpumask) < 0);
spin_lock_irq(&pool->lock);
+
+ /*
+ * XXX: CPU hotplug notifiers are weird and can call DOWN_FAILED
+ * w/o preceding DOWN_PREPARE. Work around it. CPU hotplug is
+ * being reworked and this can go away in time.
+ */
+ if (!(pool->flags & POOL_DISASSOCIATED)) {
+ spin_unlock_irq(&pool->lock);
+ return;
+ }
+
pool->flags &= ~POOL_DISASSOCIATED;
for_each_pool_worker(worker, pool) {
* attributes breaks ordering guarantee. Disallow exposing ordered
* workqueues.
*/
- if (WARN_ON(wq->flags & __WQ_ORDERED))
+ if (WARN_ON(wq->flags & __WQ_ORDERED_EXPLICIT))
return -EINVAL;
wq->wq_dev = wq_dev = kzalloc(sizeof(*wq_dev), GFP_KERNEL);
ret = device_register(&wq_dev->dev);
if (ret) {
- kfree(wq_dev);
+ put_device(&wq_dev->dev);
wq->wq_dev = NULL;
return ret;
}
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