procfs: Use all-in-one vtime aware kcpustat accessor

Now that we can read also user and guest time safely under vtime, use
the relevant accessor to fix frozen kcpustat values on nohz_full CPUs.

Reported-by: Yauheni Kaliuta <yauheni.kaliuta@redhat.com>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Wanpeng Li <wanpengli@tencent.com>
Link: https://lkml.kernel.org/r/20191121024430.19938-4-frederic@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

fs/proc/stat.c

@@ -120,20 +120,23 @@ static int show_stat(struct seq_file *p, void *v)
 	getboottime64(&boottime);
 
 	for_each_possible_cpu(i) {
-		struct kernel_cpustat *kcs = &kcpustat_cpu(i);
-
-		user += kcs->cpustat[CPUTIME_USER];
-		nice += kcs->cpustat[CPUTIME_NICE];
-		system += kcpustat_field(kcs, CPUTIME_SYSTEM, i);
-		idle += get_idle_time(kcs, i);
-		iowait += get_iowait_time(kcs, i);
-		irq += kcs->cpustat[CPUTIME_IRQ];
-		softirq += kcs->cpustat[CPUTIME_SOFTIRQ];
-		steal += kcs->cpustat[CPUTIME_STEAL];
-		guest += kcs->cpustat[CPUTIME_GUEST];
-		guest_nice += kcs->cpustat[CPUTIME_GUEST_NICE];
-		sum += kstat_cpu_irqs_sum(i);
-		sum += arch_irq_stat_cpu(i);
+		struct kernel_cpustat kcpustat;
+		u64 *cpustat = kcpustat.cpustat;
+
+		kcpustat_cpu_fetch(&kcpustat, i);
+
+		user		+= cpustat[CPUTIME_USER];
+		nice		+= cpustat[CPUTIME_NICE];
+		system		+= cpustat[CPUTIME_SYSTEM];
+		idle		+= get_idle_time(&kcpustat, i);
+		iowait		+= get_iowait_time(&kcpustat, i);
+		irq		+= cpustat[CPUTIME_IRQ];
+		softirq		+= cpustat[CPUTIME_SOFTIRQ];
+		steal		+= cpustat[CPUTIME_STEAL];
+		guest		+= cpustat[CPUTIME_GUEST];
+		guest_nice	+= cpustat[CPUTIME_USER];
+		sum		+= kstat_cpu_irqs_sum(i);
+		sum		+= arch_irq_stat_cpu(i);
 
 		for (j = 0; j < NR_SOFTIRQS; j++) {
 			unsigned int softirq_stat = kstat_softirqs_cpu(j, i);
@@ -157,19 +160,22 @@ static int show_stat(struct seq_file *p, void *v)
 	seq_putc(p, '\n');
 
 	for_each_online_cpu(i) {
-		struct kernel_cpustat *kcs = &kcpustat_cpu(i);
+		struct kernel_cpustat kcpustat;
+		u64 *cpustat = kcpustat.cpustat;
+
+		kcpustat_cpu_fetch(&kcpustat, i);
 
 		/* Copy values here to work around gcc-2.95.3, gcc-2.96 */
-		user = kcs->cpustat[CPUTIME_USER];
-		nice = kcs->cpustat[CPUTIME_NICE];
-		system = kcpustat_field(kcs, CPUTIME_SYSTEM, i);
-		idle = get_idle_time(kcs, i);
-		iowait = get_iowait_time(kcs, i);
-		irq = kcs->cpustat[CPUTIME_IRQ];
-		softirq = kcs->cpustat[CPUTIME_SOFTIRQ];
-		steal = kcs->cpustat[CPUTIME_STEAL];
-		guest = kcs->cpustat[CPUTIME_GUEST];
-		guest_nice = kcs->cpustat[CPUTIME_GUEST_NICE];
+		user		= cpustat[CPUTIME_USER];
+		nice		= cpustat[CPUTIME_NICE];
+		system		= cpustat[CPUTIME_SYSTEM];
+		idle		= get_idle_time(&kcpustat, i);
+		iowait		= get_iowait_time(&kcpustat, i);
+		irq		= cpustat[CPUTIME_IRQ];
+		softirq		= cpustat[CPUTIME_SOFTIRQ];
+		steal		= cpustat[CPUTIME_STEAL];
+		guest		= cpustat[CPUTIME_GUEST];
+		guest_nice	= cpustat[CPUTIME_USER];
 		seq_printf(p, "cpu%d", i);
 		seq_put_decimal_ull(p, " ", nsec_to_clock_t(user));
 		seq_put_decimal_ull(p, " ", nsec_to_clock_t(nice));