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>

diff --git a/Documentation/cpu-hotplug.txt b/Documentation/cpu-hotplug.txt
index a741f658a3c9d7393c9693bb4486d30473438222..fb94f5a71b688ae6fda63156a2b0bbdcf5387873 100644 (file)
--- 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 892665bb12b1ec766491222ac67c2f9103c12ef4..bb4f00c0cbe94f8a5dfe1c822a072f1c6d4de928 100644 (file)
--- 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 412e6b42986f2535ddfd5e101caaec85c76f7dc6..c4ad54e0f288cde7934c1cbbdda987ea249e8e7b 100644 (file)
--- 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 73401c820110a2a877f999c702e83d593e4f9f08..e3078ce41518aec0abb0579a5c2f9cb21315dd44 100644 (file)
--- 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 3b20613325dcbf88ef7cd7c3626d8a744b12ca4a..beb45c9c08357911a78af58f24640556b0a19240 100644 (file)
--- 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 09c315214a5ec87fdddd00f039255d69f3c01b9a..40cfd5488719b96fd6ccd8d3a890e54761d0c6c0 100644 (file)
--- 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 482aec2a96318e854aede3a385cf34eedc1da95f..96d0fd07c57d5702fe9666a587df05a2ced29c51 100644 (file)
--- 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 5322e5e54a988e8d06522f532bbbe04c5e67abd4..9dc77f14fa52042978de137751e74168972b3a42 100644 (file)
--- 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 a40247e4d462e271c2017709b725e22510bb09c7..3a3ff1c5cbefbccda9beac81917bbbdafcc6cce2 100644 (file)
--- 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 656dc3fcbbaeb0601581474f14a498d4ca514d7a..b0c4152995f8bb78664869174368f77a85bfd1fc 100644 (file)
--- 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 50f5dc46368841de3497fe96534df12b871e530b..cfaf6419d817e0a387f1c39d878f342e279818b6 100644 (file)
--- 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 c3e165c2318f16657023d7693dd6a77762945861..fd599829e72a5d49a5852272ba234be8c38accaf 100644 (file)
--- 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 86e55a9c2de60d564f2d0ba5d676aed58c3270bd..672aa68bfeac79e401d02e48ae8de545bde1aa45 100644 (file)
--- 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 319821ef78afc9e0a7488cbf9b2ea1c5853b65c1..51b5ee53571a63558cef49075de15c4dc25396a6 100644 (file)
--- 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 3ed2b4b1d6d4f1c05b557f14d1dacaedaabbd473..6489f4e24ecf118f98a457284d130973ca841130 100644 (file)
--- 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)