timer_list: Convert timer list to be a proper seq_file

When running with 4096 cores attemping to read /proc/timer_list will fail
with an ENOMEM condition.  On a sufficantly large systems the total amount
of data is more then 4mb, so it won't fit into a single buffer.  The
failure can also occur on smaller systems when memory fragmentation is
high as reported by Dave Jones.

Convert /proc/timer_list to a proper seq_file with its own iterator.  This
is a little more complex given that we have to make two passes with two
separate headers.

sysrq_timer_list_show also needed to be updated to reflect the fact that
now timer_list_show only does one cpu at at time.

Signed-off-by: Nathan Zimmer <nzimmer@sgi.com>
Reported-by: Dave Jones <davej@redhat.com>
Cc: John Stultz <johnstul@us.ibm.com>
Cc: Stephen Boyd <sboyd@codeaurora.org>
Link: http://lkml.kernel.org/r/1364345790-14577-3-git-send-email-nzimmer@sgi.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 77 insertions, 12 deletions

diff --git a/kernel/time/timer_list.c b/kernel/time/timer_list.c
index 380a58977490..3bdf28323012 100644
--- a/kernel/time/timer_list.c
+++ b/kernel/time/timer_list.c
@@ -20,6 +20,13 @@
 
 #include <asm/uaccess.h>
 
+
+struct timer_list_iter {
+        int cpu;
+        bool second_pass;
+        u64 now;
+};
+
 typedef void (*print_fn_t)(struct seq_file *m, unsigned int *classes);
 
 DECLARE_PER_CPU(struct hrtimer_cpu_base, hrtimer_bases);
@@ -247,43 +254,101 @@ static void timer_list_show_tickdevices_header(struct seq_file *m)
 }
 #endif
 
-static int timer_list_show(struct seq_file *m, void *v)
+static inline void timer_list_header(struct seq_file *m, u64 now)
 {
-        u64 now = ktime_to_ns(ktime_get());
-        int cpu;
-
         SEQ_printf(m, "Timer List Version: v0.7\n");
         SEQ_printf(m, "HRTIMER_MAX_CLOCK_BASES: %d\n", HRTIMER_MAX_CLOCK_BASES);
         SEQ_printf(m, "now at %Ld nsecs\n", (unsigned long long)now);
         SEQ_printf(m, "\n");
+}
+
+static int timer_list_show(struct seq_file *m, void *v)
+{
+        struct timer_list_iter *iter = v;
+        u64 now = ktime_to_ns(ktime_get());
+
+        if (iter->cpu == -1 && !iter->second_pass)
+                timer_list_header(m, now);
+        else if (!iter->second_pass)
+                print_cpu(m, iter->cpu, iter->now);
+#ifdef CONFIG_GENERIC_CLOCKEVENTS
+        else if (iter->cpu == -1 && iter->second_pass)
+                timer_list_show_tickdevices_header(m);
+        else
+                print_tickdevice(m, tick_get_device(iter->cpu), iter->cpu);
+#endif
+        return 0;
+}
+
+void sysrq_timer_list_show(void)
+{
+        u64 now = ktime_to_ns(ktime_get());
+        int cpu;
+
+        timer_list_header(NULL, now);
 
         for_each_online_cpu(cpu)
-                print_cpu(m, cpu, now);
+                print_cpu(NULL, cpu, now);
 
 #ifdef CONFIG_GENERIC_CLOCKEVENTS
-        timer_list_show_tickdevices_header(m);
+        timer_list_show_tickdevices_header(NULL);
         for_each_online_cpu(cpu)
-                print_tickdevice(m, tick_get_device(cpu), cpu);
+                print_tickdevice(NULL, tick_get_device(cpu), cpu);
 #endif
+        return;
+}
 
-        return 0;
+static void *timer_list_start(struct seq_file *file, loff_t *offset)
+{
+        struct timer_list_iter *iter = file->private;
+
+        if (!*offset) {
+                iter->cpu = -1;
+                iter->now = ktime_to_ns(ktime_get());
+        } else if (iter->cpu >= nr_cpu_ids) {
+#ifdef CONFIG_GENERIC_CLOCKEVENTS
+                if (!iter->second_pass) {
+                        iter->cpu = -1;
+                        iter->second_pass = true;
+                } else
+                        return NULL;
+#else
+                return NULL;
+#endif
+        }
+        return iter;
 }
 
-void sysrq_timer_list_show(void)
+static void *timer_list_next(struct seq_file *file, void *v, loff_t *offset)
 {
-        timer_list_show(NULL, NULL);
+        struct timer_list_iter *iter = file->private;
+        iter->cpu = cpumask_next(iter->cpu, cpu_online_mask);
+        ++*offset;
+        return timer_list_start(file, offset);
 }
 
+static void timer_list_stop(struct seq_file *seq, void *v)
+{
+}
+
+static const struct seq_operations timer_list_sops = {
+        .start = timer_list_start,
+        .next = timer_list_next,
+        .stop = timer_list_stop,
+        .show = timer_list_show,
+};
+
 static int timer_list_open(struct inode *inode, struct file *filp)
 {
-        return single_open(filp, timer_list_show, NULL);
+        return seq_open_private(filp, &timer_list_sops,
+                        sizeof(struct timer_list_iter));
 }
 
 static const struct file_operations timer_list_fops = {
         .open           = timer_list_open,
         .read           = seq_read,
         .llseek         = seq_lseek,
-        .release        = single_release,
+        .release        = seq_release_private,
 };
 
 static int __init init_timer_list_procfs(void)