[PATCH] minor cleanups for hotplug CPUs

Note that without CONFIG_HOTPLUG_CPU, online cpus == possible cpus, so
substitutions are a noop.

- Changes show_stat to print out stats for every possible cpu, not
  just online CPUs.

- Allocate mem in stat_open on possible, not online_cpus.

- Add conventient macros to cpu.h: especially cpu_is_offline() for
  testing if a cpu is still online.

- Add a num_possible_cpus() similar to num_online_cpus(), and define
  cpu_possible_mask for UP.

- Allow printk on down cpus once system is running.

- Mask cpumask with possible, not online cpus, for sys_getaffinity().

fs/proc/proc_misc.c

@@ -389,7 +389,7 @@ int show_stat(struct seq_file *p, void *v)
 		jiffies_to_clock_t(iowait),
 		jiffies_to_clock_t(irq),
 		jiffies_to_clock_t(softirq));
-	for_each_online_cpu(i) {
+	for_each_cpu(i) {
 		seq_printf(p, "cpu%d %u %u %u %u %u %u %u\n",
 			i,
 			jiffies_to_clock_t(kstat_cpu(i).cpustat.user),
@@ -424,7 +424,7 @@ int show_stat(struct seq_file *p, void *v)
 
 static int stat_open(struct inode *inode, struct file *file)
 {
-	unsigned size = 4096 * (1 + num_online_cpus() / 32);
+	unsigned size = 4096 * (1 + num_possible_cpus() / 32);
 	char *buf;
 	struct seq_file *m;
 	int res;

include/linux/cpu.h

@@ -21,6 +21,8 @@
 
 #include <linux/sysdev.h>
 #include <linux/node.h>
+#include <linux/compiler.h>
+#include <linux/cpumask.h>
 #include <asm/semaphore.h>
 
 struct cpu {
@@ -56,9 +58,20 @@ extern struct sysdev_class cpu_sysdev_class;
 extern struct semaphore cpucontrol;
 #define lock_cpu_hotplug()	down(&cpucontrol)
 #define unlock_cpu_hotplug()	up(&cpucontrol)
+#define lock_cpu_hotplug_interruptible() down_interruptible(&cpucontrol)
+#define hotcpu_notifier(fn, pri) {				\
+	static struct notifier_block fn##_nb = { fn, pri };	\
+	register_cpu_notifier(&fn##_nb);			\
+}
+#define cpu_is_offline(cpu) unlikely(!cpu_online(cpu))
 #else
 #define lock_cpu_hotplug()	do { } while (0)
 #define unlock_cpu_hotplug()	do { } while (0)
+#define lock_cpu_hotplug_interruptible() 0
+#define hotcpu_notifier(fn, pri)
+
+/* CPUs don't go offline once they're online w/o CONFIG_HOTPLUG_CPU */
+#define cpu_is_offline(cpu) 0
 #endif
 
 #endif /* _LINUX_CPU_H_ */

include/linux/cpumask.h

@@ -12,6 +12,7 @@ extern cpumask_t cpu_online_map;
 extern cpumask_t cpu_possible_map;
 
 #define num_online_cpus()		cpus_weight(cpu_online_map)
+#define num_possible_cpus()		cpus_weight(cpu_possible_map)
 #define cpu_online(cpu)			cpu_isset(cpu, cpu_online_map)
 #define cpu_possible(cpu)		cpu_isset(cpu, cpu_possible_map)
 
@@ -24,7 +25,9 @@ extern cpumask_t cpu_possible_map;
 #define for_each_online_cpu(cpu) for_each_cpu_mask(cpu, cpu_online_map)
 #else
 #define	cpu_online_map			cpumask_of_cpu(0)
+#define	cpu_possible_map		cpumask_of_cpu(0)
 #define num_online_cpus()		1
+#define num_possible_cpus()		1
 #define cpu_online(cpu)			({ BUG_ON((cpu) != 0); 1; })
 #define cpu_possible(cpu)		({ BUG_ON((cpu) != 0); 1; })
 

kernel/printk.c

@@ -522,7 +522,7 @@ asmlinkage int printk(const char *fmt, ...)
 			log_level_unknown = 1;
 	}
 
-	if (!cpu_online(smp_processor_id())) {
+	if (!cpu_online(smp_processor_id()) && !system_running) {
 		/*
 		 * Some console drivers may assume that per-cpu resources have
 		 * been allocated.  So don't allow them to be called by this

kernel/sched.c

@@ -2366,7 +2366,7 @@ asmlinkage long sys_sched_getaffinity(pid_t pid, unsigned int len,
 		goto out_unlock;
 
 	retval = 0;
-	cpus_and(mask, p->cpus_allowed, cpu_online_map);
+	cpus_and(mask, p->cpus_allowed, cpu_possible_map);
 
 out_unlock:
 	read_unlock(&tasklist_lock);