workqueue: protect wq->saved_max_active with wq->mutex

We're expanding wq->mutex to cover all fields specific to each
workqueue with the end goal of replacing pwq_lock which will make
locking simpler and easier to understand.

This patch makes wq->saved_max_active protected by wq->mutex instead
of pwq_lock.  As pwq_lock locking around pwq_adjust_mac_active() is no
longer necessary, this patch also replaces pwq_lock lockings of
for_each_pwq() around pwq_adjust_max_active() to wq->mutex.

tj: Rebased on top of the current dev branch.  Updated description.

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

1 files changed, 16 insertions, 17 deletions

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 9c32fd171d5c..af6087a5a10a 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -243,7 +243,7 @@ struct workqueue_struct {
         struct worker           *rescuer;       /* I: rescue worker */
 
         int                     nr_drainers;    /* WQ: drain in progress */
-        int                     saved_max_active; /* PW: saved pwq max_active */
+        int                     saved_max_active; /* WQ: saved pwq max_active */
 
 #ifdef CONFIG_SYSFS
         struct wq_device        *wq_dev;        /* I: for sysfs interface */
@@ -3579,13 +3579,13 @@ static void pwq_adjust_max_active(struct pool_workqueue *pwq)
         bool freezable = wq->flags & WQ_FREEZABLE;
 
         /* for @wq->saved_max_active */
-        lockdep_assert_held(&pwq_lock);
+        lockdep_assert_held(&wq->mutex);
 
         /* fast exit for non-freezable wqs */
         if (!freezable && pwq->max_active == wq->saved_max_active)
                 return;
 
-        spin_lock(&pwq->pool->lock);
+        spin_lock_irq(&pwq->pool->lock);
 
         if (!freezable || !(pwq->pool->flags & POOL_FREEZING)) {
                 pwq->max_active = wq->saved_max_active;
@@ -3603,7 +3603,7 @@ static void pwq_adjust_max_active(struct pool_workqueue *pwq)
                 pwq->max_active = 0;
         }
 
-        spin_unlock(&pwq->pool->lock);
+        spin_unlock_irq(&pwq->pool->lock);
 }
 
 static void init_and_link_pwq(struct pool_workqueue *pwq,
@@ -3622,7 +3622,6 @@ static void init_and_link_pwq(struct pool_workqueue *pwq,
         INIT_WORK(&pwq->unbound_release_work, pwq_unbound_release_workfn);
 
         mutex_lock(&wq->mutex);
-        spin_lock_irq(&pwq_lock);
 
         /*
          * Set the matching work_color.  This is synchronized with
@@ -3636,9 +3635,10 @@ static void init_and_link_pwq(struct pool_workqueue *pwq,
         pwq_adjust_max_active(pwq);
 
         /* link in @pwq */
+        spin_lock_irq(&pwq_lock);
         list_add_rcu(&pwq->pwqs_node, &wq->pwqs);
-
         spin_unlock_irq(&pwq_lock);
+
         mutex_unlock(&wq->mutex);
 }
 
@@ -3803,10 +3803,10 @@ struct workqueue_struct *__alloc_workqueue_key(const char *fmt,
          */
         mutex_lock(&wq_pool_mutex);
 
-        spin_lock_irq(&pwq_lock);
+        mutex_lock(&wq->mutex);
         for_each_pwq(pwq, wq)
                 pwq_adjust_max_active(pwq);
-        spin_unlock_irq(&pwq_lock);
+        mutex_unlock(&wq->mutex);
 
         list_add(&wq->list, &workqueues);
 
@@ -3917,14 +3917,14 @@ void workqueue_set_max_active(struct workqueue_struct *wq, int max_active)
 
         max_active = wq_clamp_max_active(max_active, wq->flags, wq->name);
 
-        spin_lock_irq(&pwq_lock);
+        mutex_lock(&wq->mutex);
 
         wq->saved_max_active = max_active;
 
         for_each_pwq(pwq, wq)
                 pwq_adjust_max_active(pwq);
 
-        spin_unlock_irq(&pwq_lock);
+        mutex_unlock(&wq->mutex);
 }
 EXPORT_SYMBOL_GPL(workqueue_set_max_active);
 
@@ -4287,7 +4287,7 @@ EXPORT_SYMBOL_GPL(work_on_cpu);
  * pool->worklist.
  *
  * CONTEXT:
- * Grabs and releases wq_pool_mutex, pwq_lock and pool->lock's.
+ * Grabs and releases wq_pool_mutex, wq->mutex and pool->lock's.
  */
 void freeze_workqueues_begin(void)
 {
@@ -4309,13 +4309,12 @@ void freeze_workqueues_begin(void)
                 spin_unlock_irq(&pool->lock);
         }
 
-        /* suppress further executions by setting max_active to zero */
-        spin_lock_irq(&pwq_lock);
         list_for_each_entry(wq, &workqueues, list) {
+                mutex_lock(&wq->mutex);
                 for_each_pwq(pwq, wq)
                         pwq_adjust_max_active(pwq);
+                mutex_unlock(&wq->mutex);
         }
-        spin_unlock_irq(&pwq_lock);
 
         mutex_unlock(&wq_pool_mutex);
 }
@@ -4373,7 +4372,7 @@ out_unlock:
  * frozen works are transferred to their respective pool worklists.
  *
  * CONTEXT:
- * Grabs and releases wq_pool_mutex, pwq_lock and pool->lock's.
+ * Grabs and releases wq_pool_mutex, wq->mutex and pool->lock's.
  */
 void thaw_workqueues(void)
 {
@@ -4396,12 +4395,12 @@ void thaw_workqueues(void)
         }
 
         /* restore max_active and repopulate worklist */
-        spin_lock_irq(&pwq_lock);
         list_for_each_entry(wq, &workqueues, list) {
+                mutex_lock(&wq->mutex);
                 for_each_pwq(pwq, wq)
                         pwq_adjust_max_active(pwq);
+                mutex_unlock(&wq->mutex);
         }
-        spin_unlock_irq(&pwq_lock);
 
         workqueue_freezing = false;
 out_unlock: