Re: [PATCH 3/6] workqueue: Make worker_attach/detach_pool() update worker->pool

For historical reasons, the worker attach/detach functions don't
currently manage worker->pool and the callers are manually and
inconsistently updating it.

This patch moves worker->pool updates into the worker attach/detach
functions.  This makes worker->pool consistent and clearly defines how
worker->pool updates are synchronized.

This will help later workqueue visibility improvements by allowing
safe access to workqueue information from worker->task.

Signed-off-by: Tejun Heo <tj@kernel.org>
---
 kernel/workqueue.c          | 16 ++++++++--------
 kernel/workqueue_internal.h |  2 +-
 2 files changed, 9 insertions(+), 9 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 91fe0a6..2fde50f 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c

@@ -1741,6 +1741,7 @@ static void worker_attach_to_pool(struct worker *worker,
                worker->flags |= WORKER_UNBOUND;

        list_add_tail(&worker->node, &pool->workers);
+       worker->pool = pool;

        mutex_unlock(&wq_pool_attach_mutex);
 }

@@ -1748,19 +1749,21 @@ static void worker_attach_to_pool(struct worker *worker,
 /**
  * worker_detach_from_pool() - detach a worker from its pool
  * @worker: worker which is attached to its pool
- * @pool: the pool @worker is attached to
  *
  * Undo the attaching which had been done in worker_attach_to_pool().  The
  * caller worker shouldn't access to the pool after detached except it has
  * other reference to the pool.
  */
-static void worker_detach_from_pool(struct worker *worker,
-                                   struct worker_pool *pool)
+static void worker_detach_from_pool(struct worker *worker)
 {
+       struct worker_pool *pool = worker->pool;
        struct completion *detach_completion = NULL;

        mutex_lock(&wq_pool_attach_mutex);
+
        list_del(&worker->node);
+       worker->pool = NULL;
+
        if (list_empty(&pool->workers))
                detach_completion = pool->detach_completion;
        mutex_unlock(&wq_pool_attach_mutex);

@@ -1799,7 +1802,6 @@ static struct worker *create_worker(struct worker_pool *pool)
        if (!worker)
                goto fail;

-       worker->pool = pool;
        worker->id = id;

        if (pool->cpu >= 0)

@@ -2236,7 +2238,7 @@ static int worker_thread(void *__worker)

                set_task_comm(worker->task, "kworker/dying");
                ida_simple_remove(&pool->worker_ida, worker->id);
-               worker_detach_from_pool(worker, pool);
+               worker_detach_from_pool(worker);
                kfree(worker);
                return 0;
        }

@@ -2367,7 +2369,6 @@ static int rescuer_thread(void *__rescuer)
                worker_attach_to_pool(rescuer, pool);

                spin_lock_irq(&pool->lock);
-               rescuer->pool = pool;

                /*
                 * Slurp in all works issued via this workqueue and

@@ -2417,10 +2418,9 @@ static int rescuer_thread(void *__rescuer)
                if (need_more_worker(pool))
                        wake_up_worker(pool);

-               rescuer->pool = NULL;
                spin_unlock_irq(&pool->lock);

-               worker_detach_from_pool(rescuer, pool);
+               worker_detach_from_pool(rescuer);

                spin_lock_irq(&wq_mayday_lock);
        }

diff --git a/kernel/workqueue_internal.h b/kernel/workqueue_internal.h
index d390d1b..4a182e0 100644
--- a/kernel/workqueue_internal.h
+++ b/kernel/workqueue_internal.h

@@ -37,7 +37,7 @@ struct worker {
        /* 64 bytes boundary on 64bit, 32 on 32bit */

        struct task_struct      *task;          /* I: worker task */
-       struct worker_pool      *pool;          /* I: the associated pool */
+       struct worker_pool      *pool;          /* A: the associated pool */
                                                /* L: for rescuers */