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>

3 files changed, 24 insertions, 40 deletions

diff --git a/kernel/cpu.c b/kernel/cpu.c
index b0c4152995f8..e0d3a4f56ecb 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -218,7 +218,6 @@ static int _cpu_down(unsigned int cpu, int tasks_frozen)
                 return -EINVAL;
 
         cpu_hotplug_begin();
-        raw_notifier_call_chain(&cpu_chain, CPU_LOCK_ACQUIRE, hcpu);
         err = __raw_notifier_call_chain(&cpu_chain, CPU_DOWN_PREPARE | mod,
                                         hcpu, -1, &nr_calls);
         if (err == NOTIFY_BAD) {
@@ -271,7 +270,6 @@ out_thread:
 out_allowed:
         set_cpus_allowed(current, old_allowed);
 out_release:
-        raw_notifier_call_chain(&cpu_chain, CPU_LOCK_RELEASE, hcpu);
         cpu_hotplug_done();
         return err;
 }
@@ -302,7 +300,6 @@ static int __cpuinit _cpu_up(unsigned int cpu, int tasks_frozen)
                 return -EINVAL;
 
         cpu_hotplug_begin();
-        raw_notifier_call_chain(&cpu_chain, CPU_LOCK_ACQUIRE, hcpu);
         ret = __raw_notifier_call_chain(&cpu_chain, CPU_UP_PREPARE | mod, hcpu,
                                                         -1, &nr_calls);
         if (ret == NOTIFY_BAD) {
@@ -326,7 +323,6 @@ out_notify:
         if (ret != 0)
                 __raw_notifier_call_chain(&cpu_chain,
                                 CPU_UP_CANCELED | mod, hcpu, nr_calls, NULL);
-        raw_notifier_call_chain(&cpu_chain, CPU_LOCK_RELEASE, hcpu);
         cpu_hotplug_done();
 
         return ret;
diff --git a/kernel/sched.c b/kernel/sched.c
index 672aa68bfeac..c0e2db683e29 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -439,7 +439,6 @@ struct rq {
 };
 
 static DEFINE_PER_CPU_SHARED_ALIGNED(struct rq, runqueues);
-static DEFINE_MUTEX(sched_hotcpu_mutex);
 
 static inline void check_preempt_curr(struct rq *rq, struct task_struct *p)
 {
@@ -4546,13 +4545,13 @@ long sched_setaffinity(pid_t pid, cpumask_t new_mask)
         struct task_struct *p;
         int retval;
 
-        mutex_lock(&sched_hotcpu_mutex);
+        get_online_cpus();
         read_lock(&tasklist_lock);
 
         p = find_process_by_pid(pid);
         if (!p) {
                 read_unlock(&tasklist_lock);
-                mutex_unlock(&sched_hotcpu_mutex);
+                put_online_cpus();
                 return -ESRCH;
         }
 
@@ -4592,7 +4591,7 @@ long sched_setaffinity(pid_t pid, cpumask_t new_mask)
         }
 out_unlock:
         put_task_struct(p);
-        mutex_unlock(&sched_hotcpu_mutex);
+        put_online_cpus();
         return retval;
 }
 
@@ -4649,7 +4648,7 @@ long sched_getaffinity(pid_t pid, cpumask_t *mask)
         struct task_struct *p;
         int retval;
 
-        mutex_lock(&sched_hotcpu_mutex);
+        get_online_cpus();
         read_lock(&tasklist_lock);
 
         retval = -ESRCH;
@@ -4665,7 +4664,7 @@ long sched_getaffinity(pid_t pid, cpumask_t *mask)
 
 out_unlock:
         read_unlock(&tasklist_lock);
-        mutex_unlock(&sched_hotcpu_mutex);
+        put_online_cpus();
 
         return retval;
 }
@@ -5625,9 +5624,6 @@ migration_call(struct notifier_block *nfb, unsigned long action, void *hcpu)
         struct rq *rq;
 
         switch (action) {
-        case CPU_LOCK_ACQUIRE:
-                mutex_lock(&sched_hotcpu_mutex);
-                break;
 
         case CPU_UP_PREPARE:
         case CPU_UP_PREPARE_FROZEN:
@@ -5697,9 +5693,6 @@ migration_call(struct notifier_block *nfb, unsigned long action, void *hcpu)
                 spin_unlock_irq(&rq->lock);
                 break;
 #endif
-        case CPU_LOCK_RELEASE:
-                mutex_unlock(&sched_hotcpu_mutex);
-                break;
         }
         return NOTIFY_OK;
 }
@@ -6655,10 +6648,10 @@ static int arch_reinit_sched_domains(void)
 {
         int err;
 
-        mutex_lock(&sched_hotcpu_mutex);
+        get_online_cpus();
         detach_destroy_domains(&cpu_online_map);
         err = arch_init_sched_domains(&cpu_online_map);
-        mutex_unlock(&sched_hotcpu_mutex);
+        put_online_cpus();
 
         return err;
 }
@@ -6769,12 +6762,12 @@ void __init sched_init_smp(void)
 {
         cpumask_t non_isolated_cpus;
 
-        mutex_lock(&sched_hotcpu_mutex);
+        get_online_cpus();
         arch_init_sched_domains(&cpu_online_map);
         cpus_andnot(non_isolated_cpus, cpu_possible_map, cpu_isolated_map);
         if (cpus_empty(non_isolated_cpus))
                 cpu_set(smp_processor_id(), non_isolated_cpus);
-        mutex_unlock(&sched_hotcpu_mutex);
+        put_online_cpus();
         /* XXX: Theoretical race here - CPU may be hotplugged now */
         hotcpu_notifier(update_sched_domains, 0);
 
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: