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>

15 files changed, 62 insertions, 61 deletions

diff --git a/Documentation/cpu-hotplug.txt b/Documentation/cpu-hotplug.txt
index a741f658a3c9..fb94f5a71b68 100644
--- a/Documentation/cpu-hotplug.txt
+++ b/Documentation/cpu-hotplug.txt
@@ -109,12 +109,13 @@ Never use anything other than cpumask_t to represent bitmap of CPUs.
         for_each_cpu_mask(x,mask) - Iterate over some random collection of cpu mask.
 
         #include <linux/cpu.h>
-        lock_cpu_hotplug() and unlock_cpu_hotplug():
+        get_online_cpus() and put_online_cpus():
 
-The above calls are used to inhibit cpu hotplug operations. While holding the
-cpucontrol mutex, cpu_online_map will not change. If you merely need to avoid
-cpus going away, you could also use preempt_disable() and preempt_enable()
-for those sections. Just remember the critical section cannot call any
+The above calls are used to inhibit cpu hotplug operations. While the
+cpu_hotplug.refcount is non zero, the cpu_online_map will not change.
+If you merely need to avoid cpus going away, you could also use
+preempt_disable() and preempt_enable() for those sections.
+Just remember the critical section cannot call any
 function that can sleep or schedule this process away. The preempt_disable()
 will work as long as stop_machine_run() is used to take a cpu down.
 
diff --git a/arch/mips/kernel/mips-mt-fpaff.c b/arch/mips/kernel/mips-mt-fpaff.c
index 892665bb12b1..bb4f00c0cbe9 100644
--- a/arch/mips/kernel/mips-mt-fpaff.c
+++ b/arch/mips/kernel/mips-mt-fpaff.c
@@ -58,13 +58,13 @@ asmlinkage long mipsmt_sys_sched_setaffinity(pid_t pid, unsigned int len,
         if (copy_from_user(&new_mask, user_mask_ptr, sizeof(new_mask)))
                 return -EFAULT;
 
-        lock_cpu_hotplug();
+        get_online_cpus();
         read_lock(&tasklist_lock);
 
         p = find_process_by_pid(pid);
         if (!p) {
                 read_unlock(&tasklist_lock);
-                unlock_cpu_hotplug();
+                put_online_cpus();
                 return -ESRCH;
         }
 
@@ -106,7 +106,7 @@ asmlinkage long mipsmt_sys_sched_setaffinity(pid_t pid, unsigned int len,
 
 out_unlock:
         put_task_struct(p);
-        unlock_cpu_hotplug();
+        put_online_cpus();
         return retval;
 }
 
@@ -125,7 +125,7 @@ asmlinkage long mipsmt_sys_sched_getaffinity(pid_t pid, unsigned int len,
         if (len < real_len)
                 return -EINVAL;
 
-        lock_cpu_hotplug();
+        get_online_cpus();
         read_lock(&tasklist_lock);
 
         retval = -ESRCH;
@@ -140,7 +140,7 @@ asmlinkage long mipsmt_sys_sched_getaffinity(pid_t pid, unsigned int len,
 
 out_unlock:
         read_unlock(&tasklist_lock);
-        unlock_cpu_hotplug();
+        put_online_cpus();
         if (retval)
                 return retval;
         if (copy_to_user(user_mask_ptr, &mask, real_len))
diff --git a/arch/powerpc/platforms/pseries/hotplug-cpu.c b/arch/powerpc/platforms/pseries/hotplug-cpu.c
index 412e6b42986f..c4ad54e0f288 100644
--- a/arch/powerpc/platforms/pseries/hotplug-cpu.c
+++ b/arch/powerpc/platforms/pseries/hotplug-cpu.c
@@ -153,7 +153,7 @@ static int pseries_add_processor(struct device_node *np)
         for (i = 0; i < nthreads; i++)
                 cpu_set(i, tmp);
 
-        lock_cpu_hotplug();
+        cpu_maps_update_begin();
 
         BUG_ON(!cpus_subset(cpu_present_map, cpu_possible_map));
 
@@ -190,7 +190,7 @@ static int pseries_add_processor(struct device_node *np)
         }
         err = 0;
 out_unlock:
-        unlock_cpu_hotplug();
+        cpu_maps_update_done();
         return err;
 }
 
@@ -211,7 +211,7 @@ static void pseries_remove_processor(struct device_node *np)
 
         nthreads = len / sizeof(u32);
 
-        lock_cpu_hotplug();
+        cpu_maps_update_begin();
         for (i = 0; i < nthreads; i++) {
                 for_each_present_cpu(cpu) {
                         if (get_hard_smp_processor_id(cpu) != intserv[i])
@@ -225,7 +225,7 @@ static void pseries_remove_processor(struct device_node *np)
                         printk(KERN_WARNING "Could not find cpu to remove "
                                "with physical id 0x%x\n", intserv[i]);
         }
-        unlock_cpu_hotplug();
+        cpu_maps_update_done();
 }
 
 static int pseries_smp_notifier(struct notifier_block *nb,
diff --git a/arch/powerpc/platforms/pseries/rtasd.c b/arch/powerpc/platforms/pseries/rtasd.c
index 73401c820110..e3078ce41518 100644
--- a/arch/powerpc/platforms/pseries/rtasd.c
+++ b/arch/powerpc/platforms/pseries/rtasd.c
@@ -382,7 +382,7 @@ static void do_event_scan_all_cpus(long delay)
 {
         int cpu;
 
-        lock_cpu_hotplug();
+        get_online_cpus();
         cpu = first_cpu(cpu_online_map);
         for (;;) {
                 set_cpus_allowed(current, cpumask_of_cpu(cpu));
@@ -390,15 +390,15 @@ static void do_event_scan_all_cpus(long delay)
                 set_cpus_allowed(current, CPU_MASK_ALL);
 
                 /* Drop hotplug lock, and sleep for the specified delay */
-                unlock_cpu_hotplug();
+                put_online_cpus();
                 msleep_interruptible(delay);
-                lock_cpu_hotplug();
+                get_online_cpus();
 
                 cpu = next_cpu(cpu, cpu_online_map);
                 if (cpu == NR_CPUS)
                         break;
         }
-        unlock_cpu_hotplug();
+        put_online_cpus();
 }
 
 static int rtasd(void *unused)
diff --git a/arch/x86/kernel/cpu/mtrr/main.c b/arch/x86/kernel/cpu/mtrr/main.c
index 3b20613325dc..beb45c9c0835 100644
--- a/arch/x86/kernel/cpu/mtrr/main.c
+++ b/arch/x86/kernel/cpu/mtrr/main.c
@@ -349,7 +349,7 @@ int mtrr_add_page(unsigned long base, unsigned long size,
         replace = -1;
 
         /* No CPU hotplug when we change MTRR entries */
-        lock_cpu_hotplug();
+        get_online_cpus();
         /*  Search for existing MTRR  */
         mutex_lock(&mtrr_mutex);
         for (i = 0; i < num_var_ranges; ++i) {
@@ -405,7 +405,7 @@ int mtrr_add_page(unsigned long base, unsigned long size,
         error = i;
  out:
         mutex_unlock(&mtrr_mutex);
-        unlock_cpu_hotplug();
+        put_online_cpus();
         return error;
 }
 
@@ -495,7 +495,7 @@ int mtrr_del_page(int reg, unsigned long base, unsigned long size)
 
         max = num_var_ranges;
         /* No CPU hotplug when we change MTRR entries */
-        lock_cpu_hotplug();
+        get_online_cpus();
         mutex_lock(&mtrr_mutex);
         if (reg < 0) {
                 /*  Search for existing MTRR  */
@@ -536,7 +536,7 @@ int mtrr_del_page(int reg, unsigned long base, unsigned long size)
         error = reg;
  out:
         mutex_unlock(&mtrr_mutex);
-        unlock_cpu_hotplug();
+        put_online_cpus();
         return error;
 }
 /**
diff --git a/arch/x86/kernel/microcode.c b/arch/x86/kernel/microcode.c
index 09c315214a5e..40cfd5488719 100644
--- a/arch/x86/kernel/microcode.c
+++ b/arch/x86/kernel/microcode.c
@@ -436,7 +436,7 @@ static ssize_t microcode_write (struct file *file, const char __user *buf, size_
                 return -EINVAL;
         }
 
-        lock_cpu_hotplug();
+        get_online_cpus();
         mutex_lock(&microcode_mutex);
 
         user_buffer = (void __user *) buf;
@@ -447,7 +447,7 @@ static ssize_t microcode_write (struct file *file, const char __user *buf, size_
                 ret = (ssize_t)len;
 
         mutex_unlock(&microcode_mutex);
-        unlock_cpu_hotplug();
+        put_online_cpus();
 
         return ret;
 }
@@ -658,14 +658,14 @@ static ssize_t reload_store(struct sys_device *dev, const char *buf, size_t sz)
 
                 old = current->cpus_allowed;
 
-                lock_cpu_hotplug();
+                get_online_cpus();
                 set_cpus_allowed(current, cpumask_of_cpu(cpu));
 
                 mutex_lock(&microcode_mutex);
                 if (uci->valid)
                         err = cpu_request_microcode(cpu);
                 mutex_unlock(&microcode_mutex);
-                unlock_cpu_hotplug();
+                put_online_cpus();
                 set_cpus_allowed(current, old);
         }
         if (err)
@@ -817,9 +817,9 @@ static int __init microcode_init (void)
                 return PTR_ERR(microcode_pdev);
         }
 
-        lock_cpu_hotplug();
+        get_online_cpus();
         error = sysdev_driver_register(&cpu_sysdev_class, &mc_sysdev_driver);
-        unlock_cpu_hotplug();
+        put_online_cpus();
         if (error) {
                 microcode_dev_exit();
                 platform_device_unregister(microcode_pdev);
@@ -839,9 +839,9 @@ static void __exit microcode_exit (void)
 
         unregister_hotcpu_notifier(&mc_cpu_notifier);
 
-        lock_cpu_hotplug();
+        get_online_cpus();
         sysdev_driver_unregister(&cpu_sysdev_class, &mc_sysdev_driver);
-        unlock_cpu_hotplug();
+        put_online_cpus();
 
         platform_device_unregister(microcode_pdev);
 }
diff --git a/drivers/lguest/x86/core.c b/drivers/lguest/x86/core.c
index 482aec2a9631..96d0fd07c57d 100644
--- a/drivers/lguest/x86/core.c
+++ b/drivers/lguest/x86/core.c
@@ -459,7 +459,7 @@ void __init lguest_arch_host_init(void)
 
         /* We don't need the complexity of CPUs coming and going while we're
          * doing this. */
-        lock_cpu_hotplug();
+        get_online_cpus();
         if (cpu_has_pge) { /* We have a broader idea of "global". */
                 /* Remember that this was originally set (for cleanup). */
                 cpu_had_pge = 1;
@@ -469,20 +469,20 @@ void __init lguest_arch_host_init(void)
                 /* Turn off the feature in the global feature set. */
                 clear_bit(X86_FEATURE_PGE, boot_cpu_data.x86_capability);
         }
-        unlock_cpu_hotplug();
+        put_online_cpus();
 };
 /*:*/
 
 void __exit lguest_arch_host_fini(void)
 {
         /* If we had PGE before we started, turn it back on now. */
-        lock_cpu_hotplug();
+        get_online_cpus();
         if (cpu_had_pge) {
                 set_bit(X86_FEATURE_PGE, boot_cpu_data.x86_capability);
                 /* adjust_pge's argument "1" means set PGE. */
                 on_each_cpu(adjust_pge, (void *)1, 0, 1);
         }
-        unlock_cpu_hotplug();
+        put_online_cpus();
 }
 
 
diff --git a/drivers/s390/char/sclp_config.c b/drivers/s390/char/sclp_config.c
index 5322e5e54a98..9dc77f14fa52 100644
--- a/drivers/s390/char/sclp_config.c
+++ b/drivers/s390/char/sclp_config.c
@@ -29,12 +29,12 @@ static void sclp_cpu_capability_notify(struct work_struct *work)
         struct sys_device *sysdev;
 
         printk(KERN_WARNING TAG "cpu capability changed.\n");
-        lock_cpu_hotplug();
+        get_online_cpus();
         for_each_online_cpu(cpu) {
                 sysdev = get_cpu_sysdev(cpu);
                 kobject_uevent(&sysdev->kobj, KOBJ_CHANGE);
         }
-        unlock_cpu_hotplug();
+        put_online_cpus();
 }
 
 static void sclp_conf_receiver_fn(struct evbuf_header *evbuf)
diff --git a/include/linux/cpu.h b/include/linux/cpu.h
index a40247e4d462..3a3ff1c5cbef 100644
--- a/include/linux/cpu.h
+++ b/include/linux/cpu.h
@@ -100,8 +100,8 @@ static inline void cpuhotplug_mutex_unlock(struct mutex *cpu_hp_mutex)
         mutex_unlock(cpu_hp_mutex);
 }
 
-extern void lock_cpu_hotplug(void);
-extern void unlock_cpu_hotplug(void);
+extern void get_online_cpus(void);
+extern void put_online_cpus(void);
 #define hotcpu_notifier(fn, pri) {                              \
         static struct notifier_block fn##_nb =                  \
                 { .notifier_call = fn, .priority = pri };       \
@@ -118,8 +118,8 @@ static inline void cpuhotplug_mutex_lock(struct mutex *cpu_hp_mutex)
 static inline void cpuhotplug_mutex_unlock(struct mutex *cpu_hp_mutex)
 { }
 
-#define lock_cpu_hotplug()      do { } while (0)
-#define unlock_cpu_hotplug()    do { } while (0)
+#define get_online_cpus()       do { } while (0)
+#define put_online_cpus()       do { } while (0)
 #define hotcpu_notifier(fn, pri)        do { (void)(fn); } while (0)
 /* These aren't inline functions due to a GCC bug. */
 #define register_hotcpu_notifier(nb)    ({ (void)(nb); 0; })
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;
 }
diff --git a/net/core/flow.c b/net/core/flow.c
index 3ed2b4b1d6d4..6489f4e24ecf 100644
--- a/net/core/flow.c
+++ b/net/core/flow.c
@@ -293,7 +293,7 @@ void flow_cache_flush(void)
         static DEFINE_MUTEX(flow_flush_sem);
 
         /* Don't want cpus going down or up during this. */
-        lock_cpu_hotplug();
+        get_online_cpus();
         mutex_lock(&flow_flush_sem);
         atomic_set(&info.cpuleft, num_online_cpus());
         init_completion(&info.completion);
@@ -305,7 +305,7 @@ void flow_cache_flush(void)
 
         wait_for_completion(&info.completion);
         mutex_unlock(&flow_flush_sem);
-        unlock_cpu_hotplug();
+        put_online_cpus();
 }
 
 static void __devinit flow_cache_cpu_prepare(int cpu)