workqueue: pick cwq instead of pool in __queue_work()

Currently, __queue_work() chooses the pool to queue a work item to and
then determines cwq from the target wq and the chosen pool.  This is a
bit backwards in that we can determine cwq first and simply use
cwq->pool.  This way, we can skip get_std_worker_pool() in queueing
path which will be a hurdle when implementing custom worker pools.

Update __queue_work() such that it chooses the target cwq and then use
cwq->pool instead of the other way around.  While at it, add missing
{} in an if statement.

This patch doesn't introduce any functional changes.

tj: The original patch had two get_cwq() calls - the first to
    determine the pool by doing get_cwq(cpu, wq)->pool and the second
    to determine the matching cwq from get_cwq(pool->cpu, wq).
    Updated the function such that it chooses cwq instead of pool and
    removed the second call.  Rewrote the description.

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

1 files changed, 13 insertions, 16 deletions

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 1801c37b28c4..d6fdce12ca7e 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1193,8 +1193,6 @@ static bool is_chained_work(struct workqueue_struct *wq)
 static void __queue_work(unsigned int cpu, struct workqueue_struct *wq,
                          struct work_struct *work)
 {
-        bool highpri = wq->flags & WQ_HIGHPRI;
-        struct worker_pool *pool;
         struct cpu_workqueue_struct *cwq;
         struct list_head *worklist;
         unsigned int work_flags;
@@ -1215,7 +1213,7 @@ static void __queue_work(unsigned int cpu, struct workqueue_struct *wq,
             WARN_ON_ONCE(!is_chained_work(wq)))
                 return;
 
-        /* determine pool to use */
+        /* determine the cwq to use */
         if (!(wq->flags & WQ_UNBOUND)) {
                 struct worker_pool *last_pool;
 
@@ -1228,37 +1226,36 @@ static void __queue_work(unsigned int cpu, struct workqueue_struct *wq,
                  * work needs to be queued on that cpu to guarantee
                  * non-reentrancy.
                  */
-                pool = get_std_worker_pool(cpu, highpri);
+                cwq = get_cwq(cpu, wq);
                 last_pool = get_work_pool(work);
 
-                if (last_pool && last_pool != pool) {
+                if (last_pool && last_pool != cwq->pool) {
                         struct worker *worker;
 
                         spin_lock(&last_pool->lock);
 
                         worker = find_worker_executing_work(last_pool, work);
 
-                        if (worker && worker->current_cwq->wq == wq)
-                                pool = last_pool;
-                        else {
+                        if (worker && worker->current_cwq->wq == wq) {
+                                cwq = get_cwq(last_pool->cpu, wq);
+                        } else {
                                 /* meh... not running there, queue here */
                                 spin_unlock(&last_pool->lock);
-                                spin_lock(&pool->lock);
+                                spin_lock(&cwq->pool->lock);
                         }
                 } else {
-                        spin_lock(&pool->lock);
+                        spin_lock(&cwq->pool->lock);
                 }
         } else {
-                pool = get_std_worker_pool(WORK_CPU_UNBOUND, highpri);
-                spin_lock(&pool->lock);
+                cwq = get_cwq(WORK_CPU_UNBOUND, wq);
+                spin_lock(&cwq->pool->lock);
         }
 
-        /* pool determined, get cwq and queue */
-        cwq = get_cwq(pool->cpu, wq);
+        /* cwq determined, queue */
         trace_workqueue_queue_work(req_cpu, cwq, work);
 
         if (WARN_ON(!list_empty(&work->entry))) {
-                spin_unlock(&pool->lock);
+                spin_unlock(&cwq->pool->lock);
                 return;
         }
 
@@ -1276,7 +1273,7 @@ static void __queue_work(unsigned int cpu, struct workqueue_struct *wq,
 
         insert_work(cwq, work, worklist, work_flags);
 
-        spin_unlock(&pool->lock);
+        spin_unlock(&cwq->pool->lock);
 }
 
 /**