[PATCH 2/2] fs: proc/stat: use usual seq_file ops rather than single_open

[Heiko Carstens <heiko.carstens@de.ibm.com>]

From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

Now, /proc/stat uses single_open() for showing information. This means
the all data will be gathered and buffered once to a (big) buf.

Now, /proc/stat shows stats per cpu and stats per IRQs. To get information
in once-shot, it allocates a big buffer (until KMALLOC_MAX_SIZE).

Eric Dumazet reported that the bufsize calculation doesn't take
the numner of IRQ into account and the information cannot be
got in one-shot. (By this, seq_read() will allocate buffer again
and read the whole data gain...)

This patch changes /proc/stat to use seq_open() rather than single_open()
and provides  ->start(), ->next(), ->stop(), ->show().

By this, /proc/stat will not need to take care of size of buffer.

[heiko.carstens@de.ibm.com]: This is the forward port of a patch
from KAMEZAWA Hiroyuki (https://lkml.org/lkml/2012/1/23/41).
I added a couple of simple changes like e.g. that the cpu iterator
handles 32 cpus in a batch to avoid lots of iterations.

With this patch it should not happen anymore that reading /proc/stat
fails because of a failing high order memory allocation.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
---
 fs/proc/stat.c | 278 +++++++++++++++++++++++++++++++++++++++++----------------
 1 file changed, 203 insertions(+), 75 deletions(-)

diff --git a/fs/proc/stat.c b/fs/proc/stat.c
index 3898ca5f1e92..652e255fee90 100644
--- a/fs/proc/stat.c
+++ b/fs/proc/stat.c
@@ -77,22 +77,109 @@ static u64 get_iowait_time(int cpu)
 
 #endif
 
-static int show_stat(struct seq_file *p, void *v)
+enum proc_stat_stage /* The numbers are used as *pos and iter->stage */
+{
+	SHOW_TOTAL_CPU_STAT,
+	SHOW_PERCPU_STAT,
+	SHOW_TOTAL_IRQS,
+	SHOW_IRQ_DETAILS,
+	SHOW_TIMES,
+	SHOW_TOTAL_SOFTIRQ,
+	SHOW_SOFTIRQ_DETAILS,
+	SHOW_EOL,
+	END_STATS,
+};
+
+/*
+ * To reduce the number of ->next(), ->show() calls IRQ numbers are
+ * handled in batch.
+ */
+struct seq_stat_iter {
+	int stage;
+	unsigned long jiffies;
+	int cpu_iter;
+	int irq_iter;
+	int softirq_iter;
+	/* cached information */
+	u64 irq_sum;
+	u64 softirq_sum;
+	u32 per_softirq_sums[NR_SOFTIRQS];
+};
+
+static void *proc_stat_start(struct seq_file *p, loff_t *pos)
+{
+	struct seq_stat_iter *iter = p->private;
+
+	/* At lseek(), *pos==0 is passed.(see travers() in seq_file.c */
+	if (!*pos) {
+		struct timespec boottime;
+
+		memset(iter, 0, sizeof(*iter));
+		iter->stage = SHOW_TOTAL_CPU_STAT;
+		getboottime(&boottime);
+		iter->jiffies = boottime.tv_sec;
+	}
+	if (iter->stage == END_STATS)
+		return NULL;
+	return iter;
+}
+
+static void proc_stat_stop(struct seq_file *p, void *v)
+{
+}
+
+static void *proc_stat_next(struct seq_file *p, void *v, loff_t *pos)
+{
+	struct seq_stat_iter *iter = p->private;
+	int index;
+
+	switch (iter->stage) {
+	case SHOW_TOTAL_CPU_STAT:
+		iter->stage = SHOW_PERCPU_STAT;
+		iter->cpu_iter = cpumask_first(cpu_online_mask);
+		break;
+	case SHOW_PERCPU_STAT:
+		index = cpumask_next(iter->cpu_iter, cpu_online_mask);
+		if (index >= nr_cpu_ids)
+			iter->stage = SHOW_TOTAL_IRQS;
+		else
+			iter->cpu_iter = index;
+		break;
+	case SHOW_TOTAL_IRQS:
+		iter->stage = SHOW_IRQ_DETAILS;
+		iter->irq_iter = 0;
+		break;
+	case SHOW_IRQ_DETAILS:
+		if (iter->irq_iter >= nr_irqs)
+			iter->stage = SHOW_TIMES;
+		break;
+	case SHOW_TIMES:
+		iter->stage = SHOW_TOTAL_SOFTIRQ;
+		break;
+	case SHOW_TOTAL_SOFTIRQ:
+		iter->stage = SHOW_SOFTIRQ_DETAILS;
+		break;
+	case SHOW_SOFTIRQ_DETAILS:
+		iter->stage = SHOW_EOL;
+		break;
+	case SHOW_EOL:
+		iter->stage = END_STATS;
+		return NULL;
+	default:
+		break;
+	}
+	return iter;
+}
+
+static int show_total_cpu_stat(struct seq_file *p, struct seq_stat_iter *iter)
 {
-	int i, j;
-	unsigned long jif;
 	u64 user, nice, system, idle, iowait, irq, softirq, steal;
 	u64 guest, guest_nice;
-	u64 sum = 0;
-	u64 sum_softirq = 0;
-	unsigned int per_softirq_sums[NR_SOFTIRQS] = {0};
-	struct timespec boottime;
+	int i, j;
 
-	user = nice = system = idle = iowait =
-		irq = softirq = steal = 0;
+	user = nice = system = idle = iowait = 0;
+	irq = softirq = steal = 0;
 	guest = guest_nice = 0;
-	getboottime(&boottime);
-	jif = boottime.tv_sec;
 
 	for_each_possible_cpu(i) {
 		user += kcpustat_cpu(i).cpustat[CPUTIME_USER];
@@ -105,17 +192,17 @@ static int show_stat(struct seq_file *p, void *v)
 		steal += kcpustat_cpu(i).cpustat[CPUTIME_STEAL];
 		guest += kcpustat_cpu(i).cpustat[CPUTIME_GUEST];
 		guest_nice += kcpustat_cpu(i).cpustat[CPUTIME_GUEST_NICE];
-		sum += kstat_cpu_irqs_sum(i);
-		sum += arch_irq_stat_cpu(i);
+		iter->irq_sum += kstat_cpu_irqs_sum(i);
+		iter->irq_sum += arch_irq_stat_cpu(i);
 
 		for (j = 0; j < NR_SOFTIRQS; j++) {
 			unsigned int softirq_stat = kstat_softirqs_cpu(j, i);
 
-			per_softirq_sums[j] += softirq_stat;
-			sum_softirq += softirq_stat;
+			iter->per_softirq_sums[j] += softirq_stat;
+			iter->softirq_sum += softirq_stat;
 		}
 	}
-	sum += arch_irq_stat();
+	iter->irq_sum += arch_irq_stat();
 
 	seq_puts(p, "cpu ");
 	seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(user));
@@ -129,20 +216,31 @@ static int show_stat(struct seq_file *p, void *v)
 	seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(guest));
 	seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(guest_nice));
 	seq_putc(p, '\n');
+	return 0;
+}
+
+static int show_online_cpu_stat(struct seq_file *p, struct seq_stat_iter *iter)
+{
+	u64 user, nice, system, idle, iowait, irq, softirq, steal;
+	u64 guest, guest_nice;
+	int i, cpu, index;
 
-	for_each_online_cpu(i) {
+	/* Handle 32 cpus at a time, to avoid lots of seqfile iterations. */
+	cpu = index = iter->cpu_iter;
+	for (i = 0; i < 32 && index < nr_cpu_ids; i++) {
+		cpu = index;
 		/* Copy values here to work around gcc-2.95.3, gcc-2.96 */
-		user = kcpustat_cpu(i).cpustat[CPUTIME_USER];
-		nice = kcpustat_cpu(i).cpustat[CPUTIME_NICE];
-		system = kcpustat_cpu(i).cpustat[CPUTIME_SYSTEM];
-		idle = get_idle_time(i);
-		iowait = get_iowait_time(i);
-		irq = kcpustat_cpu(i).cpustat[CPUTIME_IRQ];
-		softirq = kcpustat_cpu(i).cpustat[CPUTIME_SOFTIRQ];
-		steal = kcpustat_cpu(i).cpustat[CPUTIME_STEAL];
-		guest = kcpustat_cpu(i).cpustat[CPUTIME_GUEST];
-		guest_nice = kcpustat_cpu(i).cpustat[CPUTIME_GUEST_NICE];
-		seq_printf(p, "cpu%d", i);
+		user = kcpustat_cpu(cpu).cpustat[CPUTIME_USER];
+		nice = kcpustat_cpu(cpu).cpustat[CPUTIME_NICE];
+		system = kcpustat_cpu(cpu).cpustat[CPUTIME_SYSTEM];
+		idle = get_idle_time(cpu);
+		iowait = get_iowait_time(cpu);
+		irq = kcpustat_cpu(cpu).cpustat[CPUTIME_IRQ];
+		softirq = kcpustat_cpu(cpu).cpustat[CPUTIME_SOFTIRQ];
+		steal = kcpustat_cpu(cpu).cpustat[CPUTIME_STEAL];
+		guest = kcpustat_cpu(cpu).cpustat[CPUTIME_GUEST];
+		guest_nice = kcpustat_cpu(cpu).cpustat[CPUTIME_GUEST_NICE];
+		seq_printf(p, "cpu%d", cpu);
 		seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(user));
 		seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(nice));
 		seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(system));
@@ -154,66 +252,96 @@ static int show_stat(struct seq_file *p, void *v)
 		seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(guest));
 		seq_put_decimal_ull(p, ' ', cputime64_to_clock_t(guest_nice));
 		seq_putc(p, '\n');
+		index = cpumask_next(cpu, cpu_online_mask);
 	}
-	seq_printf(p, "intr %llu", (unsigned long long)sum);
-
-	/* sum again ? it could be updated? */
-	for_each_irq_nr(j)
-		seq_put_decimal_ull(p, ' ', kstat_irqs(j));
-
-	seq_printf(p,
-		"\nctxt %llu\n"
-		"btime %lu\n"
-		"processes %lu\n"
-		"procs_running %lu\n"
-		"procs_blocked %lu\n",
-		nr_context_switches(),
-		(unsigned long)jif,
-		total_forks,
-		nr_running(),
-		nr_iowait());
-
-	seq_printf(p, "softirq %llu", (unsigned long long)sum_softirq);
-
-	for (i = 0; i < NR_SOFTIRQS; i++)
-		seq_put_decimal_ull(p, ' ', per_softirq_sums[i]);
-	seq_putc(p, '\n');
+	iter->cpu_iter = cpu;
+	return 0;
+}
+
+static int show_irq_details(struct seq_file *p, struct seq_stat_iter *iter)
+{
+	int ret;
+
+	/*
+	 * we update iterater in ->show()...seems ugly but for avoiding
+	 * tons of function calls, print out here as much as possible
+	 */
+	do {
+		ret = seq_put_decimal_ull(p, ' ', kstat_irqs(iter->irq_iter));
+		if (!ret)
+			iter->irq_iter += 1;
+	} while (!ret && iter->irq_iter < nr_irqs);
 
 	return 0;
 }
 
+static int show_softirq_details(struct seq_file *p, struct seq_stat_iter *iter)
+{
+	int ret;
+
+	do {
+		ret = seq_put_decimal_ull(p, ' ',
+				iter->per_softirq_sums[iter->softirq_iter]);
+		if (!ret)
+			iter->softirq_iter += 1;
+	} while (!ret && iter->softirq_iter < NR_SOFTIRQS);
+	return 0;
+}
+
+static int proc_stat_show(struct seq_file *p, void *v)
+{
+	struct seq_stat_iter *iter = v;
+
+	switch (iter->stage) {
+	case SHOW_TOTAL_CPU_STAT:
+		return show_total_cpu_stat(p, iter);
+	case SHOW_PERCPU_STAT:
+		return show_online_cpu_stat(p, iter);
+	case SHOW_TOTAL_IRQS:
+		return seq_printf(p, "intr %llu",
+				  (unsigned long long)iter->irq_sum);
+	case SHOW_IRQ_DETAILS:
+		return show_irq_details(p, iter);
+	case SHOW_TIMES:
+		return seq_printf(p,
+				  "\nctxt %llu\n"
+				  "btime %lu\n"
+				  "processes %lu\n"
+				  "procs_running %lu\n"
+				  "procs_blocked %lu\n",
+				  nr_context_switches(),
+				  (unsigned long)iter->jiffies,
+				  total_forks,
+				  nr_running(),
+				  nr_iowait());
+	case SHOW_TOTAL_SOFTIRQ:
+		return seq_printf(p, "softirq %llu",
+				  (unsigned long long)iter->softirq_sum);
+	case SHOW_SOFTIRQ_DETAILS:
+		return show_softirq_details(p, iter);
+	case SHOW_EOL:
+		return seq_putc(p, '\n');
+	}
+	return 0;
+}
+
+static const struct seq_operations show_stat_op = {
+	.start = proc_stat_start,
+	.next  = proc_stat_next,
+	.stop  = proc_stat_stop,
+	.show  = proc_stat_show,
+};
+
 static int stat_open(struct inode *inode, struct file *file)
 {
-	size_t size = 1024 + 128 * num_online_cpus();
-	char *buf;
-	struct seq_file *m;
-	int res;
-
-	/* minimum size to display an interrupt count : 2 bytes */
-	size += 2 * nr_irqs;
-
-	/* don't ask for more than the kmalloc() max size */
-	if (size > KMALLOC_MAX_SIZE)
-		size = KMALLOC_MAX_SIZE;
-	buf = kmalloc(size, GFP_KERNEL);
-	if (!buf)
-		return -ENOMEM;
-
-	res = single_open(file, show_stat, NULL);
-	if (!res) {
-		m = file->private_data;
-		m->buf = buf;
-		m->size = ksize(buf);
-	} else
-		kfree(buf);
-	return res;
+	return seq_open_private(file, &show_stat_op, sizeof(struct seq_stat_iter));
 }
 
 static const struct file_operations proc_stat_operations = {
 	.open		= stat_open,
 	.read		= seq_read,
 	.llseek		= seq_lseek,
-	.release	= single_release,
+	.release	= seq_release_private,
 };
 
 static int __init proc_stat_init(void)
-- 
1.8.5.5