workqueue: implement and use pwq_adjust_max_active()

Rename pwq_set_max_active() to pwq_adjust_max_active() and move
pool_workqueue->max_active synchronization and max_active
determination logic into it.

The new function should be called with workqueue_lock held for stable
workqueue->saved_max_active, determines the current max_active value
the target pool_workqueue should be using from @wq->saved_max_active
and the state of the associated pool, and applies it with proper
synchronization.

The current two users - workqueue_set_max_active() and
thaw_workqueues() - are updated accordingly.  In addition, the manual
freezing handling in __alloc_workqueue_key() and
freeze_workqueues_begin() are replaced with calls to
pwq_adjust_max_active().

This centralizes max_active handling so that it's less error-prone.

Signed-off-by: Tejun Heo <tj@kernel.org>

1 files changed, 38 insertions, 45 deletions

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index d51928981615..9e2ec4ca415a 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -3726,23 +3726,38 @@ static void pwq_unbound_release_workfn(struct work_struct *work)
 }
 
 /**
- * pwq_set_max_active - adjust max_active of a pwq
+ * pwq_adjust_max_active - update a pwq's max_active to the current setting
  * @pwq: target pool_workqueue
- * @max_active: new max_active value.
- *
- * Set @pwq->max_active to @max_active and activate delayed works if
- * increased.
  *
- * CONTEXT:
- * spin_lock_irq(pool->lock).
+ * If @pwq isn't freezing, set @pwq->max_active to the associated
+ * workqueue's saved_max_active and activate delayed work items
+ * accordingly.  If @pwq is freezing, clear @pwq->max_active to zero.
  */
-static void pwq_set_max_active(struct pool_workqueue *pwq, int max_active)
+static void pwq_adjust_max_active(struct pool_workqueue *pwq)
 {
-        pwq->max_active = max_active;
+        struct workqueue_struct *wq = pwq->wq;
+        bool freezable = wq->flags & WQ_FREEZABLE;
+
+        /* for @wq->saved_max_active */
+        lockdep_assert_held(&workqueue_lock);
+
+        /* fast exit for non-freezable wqs */
+        if (!freezable && pwq->max_active == wq->saved_max_active)
+                return;
+
+        spin_lock(&pwq->pool->lock);
+
+        if (!freezable || !(pwq->pool->flags & POOL_FREEZING)) {
+                pwq->max_active = wq->saved_max_active;
 
-        while (!list_empty(&pwq->delayed_works) &&
-               pwq->nr_active < pwq->max_active)
-                pwq_activate_first_delayed(pwq);
+                while (!list_empty(&pwq->delayed_works) &&
+                       pwq->nr_active < pwq->max_active)
+                        pwq_activate_first_delayed(pwq);
+        } else {
+                pwq->max_active = 0;
+        }
+
+        spin_unlock(&pwq->pool->lock);
 }
 
 static void init_and_link_pwq(struct pool_workqueue *pwq,
@@ -3932,15 +3947,14 @@ struct workqueue_struct *__alloc_workqueue_key(const char *fmt,
                 goto err_destroy;
 
         /*
-         * workqueue_lock protects global freeze state and workqueues
-         * list.  Grab it, set max_active accordingly and add the new
-         * workqueue to workqueues list.
+         * workqueue_lock protects global freeze state and workqueues list.
+         * Grab it, adjust max_active and add the new workqueue to
+         * workqueues list.
          */
         spin_lock_irq(&workqueue_lock);
 
-        if (workqueue_freezing && wq->flags & WQ_FREEZABLE)
-                for_each_pwq(pwq, wq)
-                        pwq->max_active = 0;
+        for_each_pwq(pwq, wq)
+                pwq_adjust_max_active(pwq);
 
         list_add(&wq->list, &workqueues);
 
@@ -4055,17 +4069,8 @@ void workqueue_set_max_active(struct workqueue_struct *wq, int max_active)
 
         wq->saved_max_active = max_active;
 
-        for_each_pwq(pwq, wq) {
-                struct worker_pool *pool = pwq->pool;
-
-                spin_lock(&pool->lock);
-
-                if (!(wq->flags & WQ_FREEZABLE) ||
-                    !(pool->flags & POOL_FREEZING))
-                        pwq_set_max_active(pwq, max_active);
-
-                spin_unlock(&pool->lock);
-        }
+        for_each_pwq(pwq, wq)
+                pwq_adjust_max_active(pwq);
 
         spin_unlock_irq(&workqueue_lock);
 }
@@ -4358,14 +4363,8 @@ void freeze_workqueues_begin(void)
 
         /* suppress further executions by setting max_active to zero */
         list_for_each_entry(wq, &workqueues, list) {
-                if (!(wq->flags & WQ_FREEZABLE))
-                        continue;
-
-                for_each_pwq(pwq, wq) {
-                        spin_lock(&pwq->pool->lock);
-                        pwq->max_active = 0;
-                        spin_unlock(&pwq->pool->lock);
-                }
+                for_each_pwq(pwq, wq)
+                        pwq_adjust_max_active(pwq);
         }
 
         spin_unlock_irq(&workqueue_lock);
@@ -4445,14 +4444,8 @@ void thaw_workqueues(void)
 
         /* restore max_active and repopulate worklist */
         list_for_each_entry(wq, &workqueues, list) {
-                if (!(wq->flags & WQ_FREEZABLE))
-                        continue;
-
-                for_each_pwq(pwq, wq) {
-                        spin_lock(&pwq->pool->lock);
-                        pwq_set_max_active(pwq, wq->saved_max_active);
-                        spin_unlock(&pwq->pool->lock);
-                }
+                for_each_pwq(pwq, wq)
+                        pwq_adjust_max_active(pwq);
         }
 
         /* kick workers */