cpu-hotplug: replace lock_cpu_hotplug() with get_online_cpus()

Replace all lock_cpu_hotplug/unlock_cpu_hotplug from the kernel and use
get_online_cpus and put_online_cpus instead as it highlights the
refcount semantics in these operations.

The new API guarantees protection against the cpu-hotplug operation, but
it doesn't guarantee serialized access to any of the local data
structures. Hence the changes needs to be reviewed.

In case of pseries_add_processor/pseries_remove_processor, use
cpu_maps_update_begin()/cpu_maps_update_done() as we're modifying the
cpu_present_map there.

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

5 files changed, 19 insertions, 19 deletions

diff --git a/kernel/cpu.c b/kernel/cpu.c
index 656dc3fcbbae..b0c4152995f8 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -48,7 +48,7 @@ void __init cpu_hotplug_init(void)
 
 #ifdef CONFIG_HOTPLUG_CPU
 
-void lock_cpu_hotplug(void)
+void get_online_cpus(void)
 {
         might_sleep();
         if (cpu_hotplug.active_writer == current)
@@ -58,9 +58,9 @@ void lock_cpu_hotplug(void)
         mutex_unlock(&cpu_hotplug.lock);
 
 }
-EXPORT_SYMBOL_GPL(lock_cpu_hotplug);
+EXPORT_SYMBOL_GPL(get_online_cpus);
 
-void unlock_cpu_hotplug(void)
+void put_online_cpus(void)
 {
         if (cpu_hotplug.active_writer == current)
                 return;
@@ -73,7 +73,7 @@ void unlock_cpu_hotplug(void)
         mutex_unlock(&cpu_hotplug.lock);
 
 }
-EXPORT_SYMBOL_GPL(unlock_cpu_hotplug);
+EXPORT_SYMBOL_GPL(put_online_cpus);
 
 #endif  /* CONFIG_HOTPLUG_CPU */
 
@@ -110,7 +110,7 @@ void cpu_maps_update_done(void)
  *   non zero and goes to sleep again.
  *
  * However, this is very difficult to achieve in practice since
- * lock_cpu_hotplug() not an api which is called all that often.
+ * get_online_cpus() not an api which is called all that often.
  *
  */
 static void cpu_hotplug_begin(void)
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 50f5dc463688..cfaf6419d817 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -537,10 +537,10 @@ static int cpusets_overlap(struct cpuset *a, struct cpuset *b)
  *
  * Call with cgroup_mutex held.  May take callback_mutex during
  * call due to the kfifo_alloc() and kmalloc() calls.  May nest
- * a call to the lock_cpu_hotplug()/unlock_cpu_hotplug() pair.
+ * a call to the get_online_cpus()/put_online_cpus() pair.
  * Must not be called holding callback_mutex, because we must not
- * call lock_cpu_hotplug() while holding callback_mutex.  Elsewhere
- * the kernel nests callback_mutex inside lock_cpu_hotplug() calls.
+ * call get_online_cpus() while holding callback_mutex.  Elsewhere
+ * the kernel nests callback_mutex inside get_online_cpus() calls.
  * So the reverse nesting would risk an ABBA deadlock.
  *
  * The three key local variables below are:
@@ -691,9 +691,9 @@ restart:
 
 rebuild:
         /* Have scheduler rebuild sched domains */
-        lock_cpu_hotplug();
+        get_online_cpus();
         partition_sched_domains(ndoms, doms);
-        unlock_cpu_hotplug();
+        put_online_cpus();
 
 done:
         if (q && !IS_ERR(q))
@@ -1617,10 +1617,10 @@ static struct cgroup_subsys_state *cpuset_create(
  *
  * If the cpuset being removed has its flag 'sched_load_balance'
  * enabled, then simulate turning sched_load_balance off, which
- * will call rebuild_sched_domains().  The lock_cpu_hotplug()
+ * will call rebuild_sched_domains().  The get_online_cpus()
  * call in rebuild_sched_domains() must not be made while holding
  * callback_mutex.  Elsewhere the kernel nests callback_mutex inside
- * lock_cpu_hotplug() calls.  So the reverse nesting would risk an
+ * get_online_cpus() calls.  So the reverse nesting would risk an
  * ABBA deadlock.
  */
 
diff --git a/kernel/rcutorture.c b/kernel/rcutorture.c
index c3e165c2318f..fd599829e72a 100644
--- a/kernel/rcutorture.c
+++ b/kernel/rcutorture.c
@@ -726,11 +726,11 @@ static void rcu_torture_shuffle_tasks(void)
         cpumask_t tmp_mask = CPU_MASK_ALL;
         int i;
 
-        lock_cpu_hotplug();
+        get_online_cpus();
 
         /* No point in shuffling if there is only one online CPU (ex: UP) */
         if (num_online_cpus() == 1) {
-                unlock_cpu_hotplug();
+                put_online_cpus();
                 return;
         }
 
@@ -762,7 +762,7 @@ static void rcu_torture_shuffle_tasks(void)
         else
                 rcu_idle_cpu--;
 
-        unlock_cpu_hotplug();
+        put_online_cpus();
 }
 
 /* Shuffle tasks across CPUs, with the intent of allowing each CPU in the
diff --git a/kernel/sched.c b/kernel/sched.c
index 86e55a9c2de6..672aa68bfeac 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -7152,7 +7152,7 @@ static int load_balance_monitor(void *unused)
                 int i, cpu, balanced = 1;
 
                 /* Prevent cpus going down or coming up */
-                lock_cpu_hotplug();
+                get_online_cpus();
                 /* lockout changes to doms_cur[] array */
                 lock_doms_cur();
                 /*
@@ -7186,7 +7186,7 @@ static int load_balance_monitor(void *unused)
                 rcu_read_unlock();
 
                 unlock_doms_cur();
-                unlock_cpu_hotplug();
+                put_online_cpus();
 
                 if (!balanced)
                         timeout = sysctl_sched_min_bal_int_shares;
diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
index 319821ef78af..51b5ee53571a 100644
--- a/kernel/stop_machine.c
+++ b/kernel/stop_machine.c
@@ -203,13 +203,13 @@ int stop_machine_run(int (*fn)(void *), void *data, unsigned int cpu)
         int ret;
 
         /* No CPUs can come up or down during this. */
-        lock_cpu_hotplug();
+        get_online_cpus();
         p = __stop_machine_run(fn, data, cpu);
         if (!IS_ERR(p))
                 ret = kthread_stop(p);
         else
                 ret = PTR_ERR(p);
-        unlock_cpu_hotplug();
+        put_online_cpus();
 
         return ret;
 }