workqueue: simplify wq_update_unbound_numa()

wq_update_unbound_numa() is known be called with wq_pool_mutex held.

But wq_update_unbound_numa() requests wq->mutex before reading
wq->unbound_attrs, wq->numa_pwq_tbl[] and wq->dfl_pwq.  But these fields
were changed to be allowed being read with wq_pool_mutex held.  So we
simply remove the mutex_lock(&wq->mutex).

Without the dependence on the the mutex_lock(&wq->mutex), the test
of wq->unbound_attrs->no_numa can also be moved upward.

The old code need a long comment to describe the stableness of
@wq->unbound_attrs which is also guaranteed by wq_pool_mutex now,
so we don't need this such comment.

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

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index b1c222270e0e360a83504edebc7b611b81823389..4a9f65b54ee5f1db96998d598f66356f1712c077 100644 (file)
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -3708,7 +3708,8 @@ static void wq_update_unbound_numa(struct workqueue_struct *wq, int cpu,
 
        lockdep_assert_held(&wq_pool_mutex);
 
-       if (!wq_numa_enabled || !(wq->flags & WQ_UNBOUND))
+       if (!wq_numa_enabled || !(wq->flags & WQ_UNBOUND) ||
+           wq->unbound_attrs->no_numa)
                return;
 
        /*
@@ -3719,10 +3720,6 @@ static void wq_update_unbound_numa(struct workqueue_struct *wq, int cpu,
        target_attrs = wq_update_unbound_numa_attrs_buf;
        cpumask = target_attrs->cpumask;
 
-       mutex_lock(&wq->mutex);
-       if (wq->unbound_attrs->no_numa)
-               goto out_unlock;
-
        copy_workqueue_attrs(target_attrs, wq->unbound_attrs);
        pwq = unbound_pwq_by_node(wq, node);
 
@@ -3734,33 +3731,26 @@ static void wq_update_unbound_numa(struct workqueue_struct *wq, int cpu,
         */
        if (wq_calc_node_cpumask(wq->dfl_pwq->pool->attrs, node, cpu_off, cpumask)) {
                if (cpumask_equal(cpumask, pwq->pool->attrs->cpumask))
-                       goto out_unlock;
+                       return;
        } else {
                goto use_dfl_pwq;
        }
 
-       mutex_unlock(&wq->mutex);
-
        /* create a new pwq */
        pwq = alloc_unbound_pwq(wq, target_attrs);
        if (!pwq) {
                pr_warn("workqueue: allocation failed while updating NUMA affinity of \"%s\"\n",
                        wq->name);
-               mutex_lock(&wq->mutex);
                goto use_dfl_pwq;
        }
 
-       /*
-        * Install the new pwq.  As this function is called only from CPU
-        * hotplug callbacks and applying a new attrs is wrapped with
-        * get/put_online_cpus(), @wq->unbound_attrs couldn't have changed
-        * inbetween.
-        */
+       /* Install the new pwq. */
        mutex_lock(&wq->mutex);
        old_pwq = numa_pwq_tbl_install(wq, node, pwq);
        goto out_unlock;
 
 use_dfl_pwq:
+       mutex_lock(&wq->mutex);
        spin_lock_irq(&wq->dfl_pwq->pool->lock);
        get_pwq(wq->dfl_pwq);
        spin_unlock_irq(&wq->dfl_pwq->pool->lock);