sched/cpuacct: Show all possible CPUs in cpuacct output

Current code show stats of online CPUs in cpuacct.statcpus,
show stats of present cpus in cpuacct.usage(_percpu), and using
present CPUs for setting cpuacct.usage.

It will cause inconsistent result when a CPU is online or offline
or hotpluged.

We should always use possible CPUs to avoid above problem.

Here are the contents of a cpuacct.usage_percpu sysfs file,
on a 4 CPU system with maxcpus=32:

Before the patch:
 # cat cpuacct.usage_percpu
 2456565 411435 1052897 832584

After the patch:
 # cat cpuacct.usage_percpu
 2456565 411435 1052897 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Zhao Lei <zhaolei@cn.fujitsu.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Tejun Heo <htejun@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/a11d56cef12d0b4807f8be3a46bf9798c3014d59.1458635566.git.zhaolei@cn.fujitsu.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

kernel/sched/cpuacct.c

@@ -138,7 +138,7 @@ static u64 cpuusage_read(struct cgroup_subsys_state *css, struct cftype *cft)
 	u64 totalcpuusage = 0;
 	int i;
 
-	for_each_present_cpu(i)
+	for_each_possible_cpu(i)
 		totalcpuusage += cpuacct_cpuusage_read(ca, i);
 
 	return totalcpuusage;
@@ -159,7 +159,7 @@ static int cpuusage_write(struct cgroup_subsys_state *css, struct cftype *cft,
 		goto out;
 	}
 
-	for_each_present_cpu(i)
+	for_each_possible_cpu(i)
 		cpuacct_cpuusage_write(ca, i, 0);
 
 out:
@@ -172,7 +172,7 @@ static int cpuacct_percpu_seq_show(struct seq_file *m, void *V)
 	u64 percpu;
 	int i;
 
-	for_each_present_cpu(i) {
+	for_each_possible_cpu(i) {
 		percpu = cpuacct_cpuusage_read(ca, i);
 		seq_printf(m, "%llu ", (unsigned long long) percpu);
 	}
@@ -191,7 +191,7 @@ static int cpuacct_stats_show(struct seq_file *sf, void *v)
 	int cpu;
 	s64 val = 0;
 
-	for_each_online_cpu(cpu) {
+	for_each_possible_cpu(cpu) {
 		struct kernel_cpustat *kcpustat = per_cpu_ptr(ca->cpustat, cpu);
 		val += kcpustat->cpustat[CPUTIME_USER];
 		val += kcpustat->cpustat[CPUTIME_NICE];
@@ -200,7 +200,7 @@ static int cpuacct_stats_show(struct seq_file *sf, void *v)
 	seq_printf(sf, "%s %lld\n", cpuacct_stat_desc[CPUACCT_STAT_USER], val);
 
 	val = 0;
-	for_each_online_cpu(cpu) {
+	for_each_possible_cpu(cpu) {
 		struct kernel_cpustat *kcpustat = per_cpu_ptr(ca->cpustat, cpu);
 		val += kcpustat->cpustat[CPUTIME_SYSTEM];
 		val += kcpustat->cpustat[CPUTIME_IRQ];