[PATCH] workqueue: remove lock_cpu_hotplug()

Use a private lock instead.  It protects all per-cpu data structures in
workqueue.c, including the workqueues list.

Fix a bug in schedule_on_each_cpu(): it was forgetting to lock down the
per-cpu resources.

Unfixed long-standing bug: if someone unplugs the CPU identified by
`singlethread_cpu' the kernel will get very sick.

Cc: Dave Jones <davej@codemonkey.org.uk>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 21 insertions, 12 deletions

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 448e8f7b342d..835fe28b87a8 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -68,7 +68,7 @@ struct workqueue_struct {
 
 /* All the per-cpu workqueues on the system, for hotplug cpu to add/remove
    threads to each one as cpus come/go. */
-static DEFINE_SPINLOCK(workqueue_lock);
+static DEFINE_MUTEX(workqueue_mutex);
 static LIST_HEAD(workqueues);
 
 static int singlethread_cpu;
@@ -320,10 +320,10 @@ void fastcall flush_workqueue(struct workqueue_struct *wq)
         } else {
                 int cpu;
 
-                lock_cpu_hotplug();
+                mutex_lock(&workqueue_mutex);
                 for_each_online_cpu(cpu)
                         flush_cpu_workqueue(per_cpu_ptr(wq->cpu_wq, cpu));
-                unlock_cpu_hotplug();
+                mutex_unlock(&workqueue_mutex);
         }
 }
 EXPORT_SYMBOL_GPL(flush_workqueue);
@@ -371,8 +371,7 @@ struct workqueue_struct *__create_workqueue(const char *name,
         }
 
         wq->name = name;
-        /* We don't need the distraction of CPUs appearing and vanishing. */
-        lock_cpu_hotplug();
+        mutex_lock(&workqueue_mutex);
         if (singlethread) {
                 INIT_LIST_HEAD(&wq->list);
                 p = create_workqueue_thread(wq, singlethread_cpu);
@@ -381,9 +380,7 @@ struct workqueue_struct *__create_workqueue(const char *name,
                 else
                         wake_up_process(p);
         } else {
-                spin_lock(&workqueue_lock);
                 list_add(&wq->list, &workqueues);
-                spin_unlock(&workqueue_lock);
                 for_each_online_cpu(cpu) {
                         p = create_workqueue_thread(wq, cpu);
                         if (p) {
@@ -393,7 +390,7 @@ struct workqueue_struct *__create_workqueue(const char *name,
                                 destroy = 1;
                 }
         }
-        unlock_cpu_hotplug();
+        mutex_unlock(&workqueue_mutex);
 
         /*
          * Was there any error during startup? If yes then clean up:
@@ -434,17 +431,15 @@ void destroy_workqueue(struct workqueue_struct *wq)
         flush_workqueue(wq);
 
         /* We don't need the distraction of CPUs appearing and vanishing. */
-        lock_cpu_hotplug();
+        mutex_lock(&workqueue_mutex);
         if (is_single_threaded(wq))
                 cleanup_workqueue_thread(wq, singlethread_cpu);
         else {
                 for_each_online_cpu(cpu)
                         cleanup_workqueue_thread(wq, cpu);
-                spin_lock(&workqueue_lock);
                 list_del(&wq->list);
-                spin_unlock(&workqueue_lock);
         }
-        unlock_cpu_hotplug();
+        mutex_unlock(&workqueue_mutex);
         free_percpu(wq->cpu_wq);
         kfree(wq);
 }
@@ -515,11 +510,13 @@ int schedule_on_each_cpu(void (*func)(void *info), void *info)
         if (!works)
                 return -ENOMEM;
 
+        mutex_lock(&workqueue_mutex);
         for_each_online_cpu(cpu) {
                 INIT_WORK(per_cpu_ptr(works, cpu), func, info);
                 __queue_work(per_cpu_ptr(keventd_wq->cpu_wq, cpu),
                                 per_cpu_ptr(works, cpu));
         }
+        mutex_unlock(&workqueue_mutex);
         flush_workqueue(keventd_wq);
         free_percpu(works);
         return 0;
@@ -635,6 +632,7 @@ static int __devinit workqueue_cpu_callback(struct notifier_block *nfb,
 
         switch (action) {
         case CPU_UP_PREPARE:
+                mutex_lock(&workqueue_mutex);
                 /* Create a new workqueue thread for it. */
                 list_for_each_entry(wq, &workqueues, list) {
                         if (!create_workqueue_thread(wq, hotcpu)) {
@@ -653,6 +651,7 @@ static int __devinit workqueue_cpu_callback(struct notifier_block *nfb,
                         kthread_bind(cwq->thread, hotcpu);
                         wake_up_process(cwq->thread);
                 }
+                mutex_unlock(&workqueue_mutex);
                 break;
 
         case CPU_UP_CANCELED:
@@ -664,6 +663,15 @@ static int __devinit workqueue_cpu_callback(struct notifier_block *nfb,
                                      any_online_cpu(cpu_online_map));
                         cleanup_workqueue_thread(wq, hotcpu);
                 }
+                mutex_unlock(&workqueue_mutex);
+                break;
+
+        case CPU_DOWN_PREPARE:
+                mutex_lock(&workqueue_mutex);
+                break;
+
+        case CPU_DOWN_FAILED:
+                mutex_unlock(&workqueue_mutex);
                 break;
 
         case CPU_DEAD:
@@ -671,6 +679,7 @@ static int __devinit workqueue_cpu_callback(struct notifier_block *nfb,
                         cleanup_workqueue_thread(wq, hotcpu);
                 list_for_each_entry(wq, &workqueues, list)
                         take_over_work(wq, hotcpu);
+                mutex_unlock(&workqueue_mutex);
                 break;
         }