workqueue: convert worker_idr to worker_ida

We no longer iterate workers via worker_idr and worker_idr is used
only for allocating/freeing ID, so we can convert it to worker_ida.

By using ida_simple_get/remove(), worker_ida doesn't require external
synchronization, so we don't need manager_mutex to protect it and the
ID-removal code is allowed to be moved out from
worker_detach_from_pool().

In a later patch, worker_detach_from_pool() will be used in rescuers
which don't have IDs, so we move the ID-removal code out from
worker_detach_from_pool() into worker_thread().

tj: Minor description updates.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

1 files changed, 8 insertions, 12 deletions

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index a6c38b717957..092f2098746d 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -161,10 +161,11 @@ struct worker_pool {
         /* see manage_workers() for details on the two manager mutexes */
         struct mutex            manager_arb;    /* manager arbitration */
         struct mutex            manager_mutex;  /* manager exclusion */
-        struct idr              worker_idr;     /* M: worker IDs */
         struct list_head        workers;        /* M: attached workers */
         struct completion       *detach_completion; /* all workers detached */
 
+        struct ida              worker_ida;     /* worker IDs for task name */
+
         struct workqueue_attrs  *attrs;         /* I: worker attributes */
         struct hlist_node       hash_node;      /* PL: unbound_pool_hash node */
         int                     refcnt;         /* PL: refcnt for unbound pools */
@@ -1696,7 +1697,6 @@ static void worker_detach_from_pool(struct worker *worker,
         struct completion *detach_completion = NULL;
 
         mutex_lock(&pool->manager_mutex);
-        idr_remove(&pool->worker_idr, worker->id);
         list_del(&worker->node);
         if (list_empty(&pool->workers))
                 detach_completion = pool->detach_completion;
@@ -1727,11 +1727,8 @@ static struct worker *create_worker(struct worker_pool *pool)
 
         lockdep_assert_held(&pool->manager_mutex);
 
-        /*
-         * ID is needed to determine kthread name.  Allocate ID first
-         * without installing the pointer.
-         */
-        id = idr_alloc(&pool->worker_idr, NULL, 0, 0, GFP_KERNEL);
+        /* ID is needed to determine kthread name */
+        id = ida_simple_get(&pool->worker_ida, 0, 0, GFP_KERNEL);
         if (id < 0)
                 goto fail;
 
@@ -1772,8 +1769,6 @@ static struct worker *create_worker(struct worker_pool *pool)
         if (pool->flags & POOL_DISASSOCIATED)
                 worker->flags |= WORKER_UNBOUND;
 
-        /* successful, commit the pointer to idr */
-        idr_replace(&pool->worker_idr, worker, worker->id);
         /* successful, attach the worker to the pool */
         list_add_tail(&worker->node, &pool->workers);
 
@@ -1781,7 +1776,7 @@ static struct worker *create_worker(struct worker_pool *pool)
 
 fail:
         if (id >= 0)
-                idr_remove(&pool->worker_idr, id);
+                ida_simple_remove(&pool->worker_ida, id);
         kfree(worker);
         return NULL;
 }
@@ -2250,6 +2245,7 @@ woke_up:
                 worker->task->flags &= ~PF_WQ_WORKER;
 
                 set_task_comm(worker->task, "kworker/dying");
+                ida_simple_remove(&pool->worker_ida, worker->id);
                 worker_detach_from_pool(worker, pool);
                 kfree(worker);
                 return 0;
@@ -3486,9 +3482,9 @@ static int init_worker_pool(struct worker_pool *pool)
 
         mutex_init(&pool->manager_arb);
         mutex_init(&pool->manager_mutex);
-        idr_init(&pool->worker_idr);
         INIT_LIST_HEAD(&pool->workers);
 
+        ida_init(&pool->worker_ida);
         INIT_HLIST_NODE(&pool->hash_node);
         pool->refcnt = 1;
 
@@ -3503,7 +3499,7 @@ static void rcu_free_pool(struct rcu_head *rcu)
 {
         struct worker_pool *pool = container_of(rcu, struct worker_pool, rcu);
 
-        idr_destroy(&pool->worker_idr);
+        ida_destroy(&pool->worker_ida);
         free_workqueue_attrs(pool->attrs);
         kfree(pool);
 }