workqueue: convert worker_pool->worker_ida to idr and implement for_each_pool_worker()
Make worker_ida an idr - worker_idr and use it to implement
for_each_pool_worker() which will be used to simplify worker rebinding
on CPU_ONLINE.
pool->worker_idr is protected by both pool->manager_mutex and
pool->lock so that it can be iterated while holding either lock.
* create_worker() allocates ID without installing worker pointer and
installs the pointer later using idr_replace(). This is because
worker ID is needed when creating the actual task to name it and the
new worker shouldn't be visible to iterations before fully
initialized.
* In destroy_worker(), ID removal is moved before kthread_stop().
This is again to guarantee that only fully working workers are
visible to for_each_pool_worker().
Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 39a591f..384ff34 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -119,6 +119,9 @@
*
* F: wq->flush_mutex protected.
*
+ * MG: pool->manager_mutex and pool->lock protected. Writes require both
+ * locks. Reads can happen under either lock.
+ *
* WQ: wq_mutex protected.
*
* WR: wq_mutex protected for writes. Sched-RCU protected for reads.
@@ -156,7 +159,7 @@
/* see manage_workers() for details on the two manager mutexes */
struct mutex manager_arb; /* manager arbitration */
struct mutex manager_mutex; /* manager exclusion */
- struct ida worker_ida; /* L: for worker IDs */
+ struct idr worker_idr; /* MG: worker IDs and iteration */
struct workqueue_attrs *attrs; /* I: worker attributes */
struct hlist_node hash_node; /* WQ: unbound_pool_hash node */
@@ -299,6 +302,15 @@
lockdep_is_held(&pwq_lock), \
"sched RCU or pwq_lock should be held")
+#ifdef CONFIG_LOCKDEP
+#define assert_manager_or_pool_lock(pool) \
+ WARN_ONCE(!lockdep_is_held(&(pool)->manager_mutex) && \
+ !lockdep_is_held(&(pool)->lock), \
+ "pool->manager_mutex or ->lock should be held")
+#else
+#define assert_manager_or_pool_lock(pool) do { } while (0)
+#endif
+
#define for_each_cpu_worker_pool(pool, cpu) \
for ((pool) = &per_cpu(cpu_worker_pools, cpu)[0]; \
(pool) < &per_cpu(cpu_worker_pools, cpu)[NR_STD_WORKER_POOLS]; \
@@ -325,6 +337,22 @@
else
/**
+ * for_each_pool_worker - iterate through all workers of a worker_pool
+ * @worker: iteration cursor
+ * @wi: integer used for iteration
+ * @pool: worker_pool to iterate workers of
+ *
+ * This must be called with either @pool->manager_mutex or ->lock held.
+ *
+ * The if/else clause exists only for the lockdep assertion and can be
+ * ignored.
+ */
+#define for_each_pool_worker(worker, wi, pool) \
+ idr_for_each_entry(&(pool)->worker_idr, (worker), (wi)) \
+ if (({ assert_manager_or_pool_lock((pool)); false; })) { } \
+ else
+
+/**
* for_each_pwq - iterate through all pool_workqueues of the specified workqueue
* @pwq: iteration cursor
* @wq: the target workqueue
@@ -1723,14 +1751,19 @@
lockdep_assert_held(&pool->manager_mutex);
+ /*
+ * ID is needed to determine kthread name. Allocate ID first
+ * without installing the pointer.
+ */
+ idr_preload(GFP_KERNEL);
spin_lock_irq(&pool->lock);
- while (ida_get_new(&pool->worker_ida, &id)) {
- spin_unlock_irq(&pool->lock);
- if (!ida_pre_get(&pool->worker_ida, GFP_KERNEL))
- goto fail;
- spin_lock_irq(&pool->lock);
- }
+
+ id = idr_alloc(&pool->worker_idr, NULL, 0, 0, GFP_NOWAIT);
+
spin_unlock_irq(&pool->lock);
+ idr_preload_end();
+ if (id < 0)
+ goto fail;
worker = alloc_worker();
if (!worker)
@@ -1768,11 +1801,17 @@
if (pool->flags & POOL_DISASSOCIATED)
worker->flags |= WORKER_UNBOUND;
+ /* successful, commit the pointer to idr */
+ spin_lock_irq(&pool->lock);
+ idr_replace(&pool->worker_idr, worker, worker->id);
+ spin_unlock_irq(&pool->lock);
+
return worker;
+
fail:
if (id >= 0) {
spin_lock_irq(&pool->lock);
- ida_remove(&pool->worker_ida, id);
+ idr_remove(&pool->worker_idr, id);
spin_unlock_irq(&pool->lock);
}
kfree(worker);
@@ -1832,7 +1871,6 @@
static void destroy_worker(struct worker *worker)
{
struct worker_pool *pool = worker->pool;
- int id = worker->id;
lockdep_assert_held(&pool->manager_mutex);
lockdep_assert_held(&pool->lock);
@@ -1850,13 +1888,14 @@
list_del_init(&worker->entry);
worker->flags |= WORKER_DIE;
+ idr_remove(&pool->worker_idr, worker->id);
+
spin_unlock_irq(&pool->lock);
kthread_stop(worker->task);
kfree(worker);
spin_lock_irq(&pool->lock);
- ida_remove(&pool->worker_ida, id);
}
static void idle_worker_timeout(unsigned long __pool)
@@ -3482,7 +3521,7 @@
mutex_init(&pool->manager_arb);
mutex_init(&pool->manager_mutex);
- ida_init(&pool->worker_ida);
+ idr_init(&pool->worker_idr);
INIT_HLIST_NODE(&pool->hash_node);
pool->refcnt = 1;
@@ -3498,7 +3537,7 @@
{
struct worker_pool *pool = container_of(rcu, struct worker_pool, rcu);
- ida_destroy(&pool->worker_ida);
+ idr_destroy(&pool->worker_idr);
free_workqueue_attrs(pool->attrs);
kfree(pool);
}