cpu-hotplug: replace per-subsystem mutexes with get_online_cpus()

This patch converts the known per-subsystem mutexes to get_online_cpus
put_online_cpus. It also eliminates the CPU_LOCK_ACQUIRE and
CPU_LOCK_RELEASE hotplug notification events.

Signed-off-by: Gautham  R Shenoy <ego@in.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 15 insertions, 20 deletions

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 8db0b597509e..52db48e7f6e7 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -67,9 +67,8 @@ struct workqueue_struct {
 #endif
 };
 
-/* All the per-cpu workqueues on the system, for hotplug cpu to add/remove
-   threads to each one as cpus come/go. */
-static DEFINE_MUTEX(workqueue_mutex);
+/* Serializes the accesses to the list of workqueues. */
+static DEFINE_SPINLOCK(workqueue_lock);
 static LIST_HEAD(workqueues);
 
 static int singlethread_cpu __read_mostly;
@@ -592,8 +591,6 @@ EXPORT_SYMBOL(schedule_delayed_work_on);
  * Returns zero on success.
  * Returns -ve errno on failure.
  *
- * Appears to be racy against CPU hotplug.
- *
  * schedule_on_each_cpu() is very slow.
  */
 int schedule_on_each_cpu(work_func_t func)
@@ -605,7 +602,7 @@ int schedule_on_each_cpu(work_func_t func)
         if (!works)
                 return -ENOMEM;
 
-        preempt_disable();              /* CPU hotplug */
+        get_online_cpus();
         for_each_online_cpu(cpu) {
                 struct work_struct *work = per_cpu_ptr(works, cpu);
 
@@ -613,8 +610,8 @@ int schedule_on_each_cpu(work_func_t func)
                 set_bit(WORK_STRUCT_PENDING, work_data_bits(work));
                 __queue_work(per_cpu_ptr(keventd_wq->cpu_wq, cpu), work);
         }
-        preempt_enable();
         flush_workqueue(keventd_wq);
+        put_online_cpus();
         free_percpu(works);
         return 0;
 }
@@ -750,8 +747,10 @@ struct workqueue_struct *__create_workqueue_key(const char *name,
                 err = create_workqueue_thread(cwq, singlethread_cpu);
                 start_workqueue_thread(cwq, -1);
         } else {
-                mutex_lock(&workqueue_mutex);
+                get_online_cpus();
+                spin_lock(&workqueue_lock);
                 list_add(&wq->list, &workqueues);
+                spin_unlock(&workqueue_lock);
 
                 for_each_possible_cpu(cpu) {
                         cwq = init_cpu_workqueue(wq, cpu);
@@ -760,7 +759,7 @@ struct workqueue_struct *__create_workqueue_key(const char *name,
                         err = create_workqueue_thread(cwq, cpu);
                         start_workqueue_thread(cwq, cpu);
                 }
-                mutex_unlock(&workqueue_mutex);
+                put_online_cpus();
         }
 
         if (err) {
@@ -775,7 +774,7 @@ static void cleanup_workqueue_thread(struct cpu_workqueue_struct *cwq, int cpu)
 {
         /*
          * Our caller is either destroy_workqueue() or CPU_DEAD,
-         * workqueue_mutex protects cwq->thread
+         * get_online_cpus() protects cwq->thread.
          */
         if (cwq->thread == NULL)
                 return;
@@ -810,9 +809,11 @@ void destroy_workqueue(struct workqueue_struct *wq)
         struct cpu_workqueue_struct *cwq;
         int cpu;
 
-        mutex_lock(&workqueue_mutex);
+        get_online_cpus();
+        spin_lock(&workqueue_lock);
         list_del(&wq->list);
-        mutex_unlock(&workqueue_mutex);
+        spin_unlock(&workqueue_lock);
+        put_online_cpus();
 
         for_each_cpu_mask(cpu, *cpu_map) {
                 cwq = per_cpu_ptr(wq->cpu_wq, cpu);
@@ -835,13 +836,6 @@ static int __devinit workqueue_cpu_callback(struct notifier_block *nfb,
         action &= ~CPU_TASKS_FROZEN;
 
         switch (action) {
-        case CPU_LOCK_ACQUIRE:
-                mutex_lock(&workqueue_mutex);
-                return NOTIFY_OK;
-
-        case CPU_LOCK_RELEASE:
-                mutex_unlock(&workqueue_mutex);
-                return NOTIFY_OK;
 
         case CPU_UP_PREPARE:
                 cpu_set(cpu, cpu_populated_map);
@@ -854,7 +848,8 @@ static int __devinit workqueue_cpu_callback(struct notifier_block *nfb,
                 case CPU_UP_PREPARE:
                         if (!create_workqueue_thread(cwq, cpu))
                                 break;
-                        printk(KERN_ERR "workqueue for %i failed\n", cpu);
+                        printk(KERN_ERR "workqueue [%s] for %i failed\n",
+                                wq->name, cpu);
                         return NOTIFY_BAD;
 
                 case CPU_ONLINE: