workqueue: remove workqueue_struct->pool_wq.single

workqueue->pool_wq union is used to point either to percpu pwqs
(pool_workqueues) or single unbound pwq.  As the first pwq can be
accessed via workqueue->pwqs list, there's no reason for the single
pointer anymore.

Use list_first_entry(workqueue->pwqs) to access the unbound pwq and
drop workqueue->pool_wq.single pointer and the pool_wq union.  It
simplifies the code and eases implementing multiple unbound pools w/
custom attributes.

This patch doesn't introduce any visible behavior changes.

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

1 files changed, 12 insertions, 14 deletions

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 73c5f68065b5..acee7b525d51 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -188,11 +188,7 @@ struct wq_flusher {
  */
 struct workqueue_struct {
         unsigned int            flags;          /* W: WQ_* flags */
-        union {
-                struct pool_workqueue __percpu          *pcpu;
-                struct pool_workqueue                   *single;
-                unsigned long                           v;
-        } pool_wq;                              /* I: pwq's */
+        struct pool_workqueue __percpu *cpu_pwqs; /* I: per-cpu pwq's */
         struct list_head        pwqs;           /* I: all pwqs of this wq */
         struct list_head        list;           /* W: list of all workqueues */
 
@@ -471,9 +467,11 @@ static struct pool_workqueue *get_pwq(int cpu, struct workqueue_struct *wq)
 {
         if (!(wq->flags & WQ_UNBOUND)) {
                 if (likely(cpu < nr_cpu_ids))
-                        return per_cpu_ptr(wq->pool_wq.pcpu, cpu);
-        } else if (likely(cpu == WORK_CPU_UNBOUND))
-                return wq->pool_wq.single;
+                        return per_cpu_ptr(wq->cpu_pwqs, cpu);
+        } else if (likely(cpu == WORK_CPU_UNBOUND)) {
+                return list_first_entry(&wq->pwqs, struct pool_workqueue,
+                                        pwqs_node);
+        }
         return NULL;
 }
 
@@ -3085,8 +3083,8 @@ static int alloc_and_link_pwqs(struct workqueue_struct *wq)
         int cpu;
 
         if (!(wq->flags & WQ_UNBOUND)) {
-                wq->pool_wq.pcpu = alloc_percpu(struct pool_workqueue);
-                if (!wq->pool_wq.pcpu)
+                wq->cpu_pwqs = alloc_percpu(struct pool_workqueue);
+                if (!wq->cpu_pwqs)
                         return -ENOMEM;
 
                 for_each_possible_cpu(cpu) {
@@ -3102,7 +3100,6 @@ static int alloc_and_link_pwqs(struct workqueue_struct *wq)
                 if (!pwq)
                         return -ENOMEM;
 
-                wq->pool_wq.single = pwq;
                 pwq->pool = get_std_worker_pool(WORK_CPU_UNBOUND, highpri);
                 list_add_tail(&pwq->pwqs_node, &wq->pwqs);
         }
@@ -3113,9 +3110,10 @@ static int alloc_and_link_pwqs(struct workqueue_struct *wq)
 static void free_pwqs(struct workqueue_struct *wq)
 {
         if (!(wq->flags & WQ_UNBOUND))
-                free_percpu(wq->pool_wq.pcpu);
-        else
-                kmem_cache_free(pwq_cache, wq->pool_wq.single);
+                free_percpu(wq->cpu_pwqs);
+        else if (!list_empty(&wq->pwqs))
+                kmem_cache_free(pwq_cache, list_first_entry(&wq->pwqs,
+                                        struct pool_workqueue, pwqs_node));
 }
 
 static int wq_clamp_max_active(int max_active, unsigned int flags,