[PATCHv2 2/2] watchdog/softlockup: report the most frequent interrupts

[Bitao Hu]

When the watchdog determines that the current soft lockup is due
to an interrupt storm based on CPU utilization, reporting the
most frequent interrupts could be good enough for further
troubleshooting.

Below is an example of interrupt storm. The call tree does not
provide useful information, but we can analyze which interrupt
caused the soft lockup by comparing the counts of interrupts.

[ 2987.488075] watchdog: BUG: soft lockup - CPU#9 stuck for 23s! [kworker/9:1:214]
[ 2987.488607] CPU#9 Utilization every 4s during lockup:
[ 2987.488941]  #1:   0% system,          0% softirq,   100% hardirq,     0% idle
[ 2987.489357]  #2:   0% system,          0% softirq,   100% hardirq,     0% idle
[ 2987.489771]  #3:   0% system,          0% softirq,   100% hardirq,     0% idle
[ 2987.490186]  #4:   0% system,          0% softirq,   100% hardirq,     0% idle
[ 2987.490601]  #5:   0% system,          0% softirq,   100% hardirq,     0% idle
[ 2987.491034] CPU#9 Detect HardIRQ Time exceeds 50%. Most frequent HardIRQs:
[ 2987.491493]  #1: 330985      irq#7(IPI)
[ 2987.491743]  #2: 5000        irq#10(arch_timer)
[ 2987.492039]  #3: 9           irq#91(nvme0q2)
[ 2987.492318]  #4: 3           irq#118(virtio1-output.12)
..
[ 2987.492728] Call trace:
[ 2987.492729]  __do_softirq+0xa8/0x364

Signed-off-by: Bitao Hu <yaoma@xxxxxxxxxxxxxxxxx>
---
 kernel/watchdog.c | 150 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 150 insertions(+)

diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 0efe9604c3c2..38fb18e17d71 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -25,6 +25,9 @@
 #include <linux/stop_machine.h>
 #include <linux/kernel_stat.h>
 #include <linux/math64.h>
+#include <linux/irq.h>
+#include <linux/bitops.h>
+#include <linux/irqdesc.h>
 
 #include <asm/irq_regs.h>
 #include <linux/kvm_para.h>
@@ -431,11 +434,15 @@ void touch_softlockup_watchdog_sync(void)
 	__this_cpu_write(watchdog_report_ts, SOFTLOCKUP_DELAY_REPORT);
 }
 
+static void set_potential_softlockup(unsigned long now, unsigned long touch_ts);
+
 static int is_softlockup(unsigned long touch_ts,
 			 unsigned long period_ts,
 			 unsigned long now)
 {
 	if ((watchdog_enabled & WATCHDOG_SOFTOCKUP_ENABLED) && watchdog_thresh) {
+		/* Softlockup may occur in the current period */
+		set_potential_softlockup(now, period_ts);
 		/* Warn about unreasonable delays. */
 		if (time_after(now, period_ts + get_softlockup_thresh()))
 			return now - touch_ts;
@@ -457,6 +464,8 @@ static enum cpu_usage_stat idx_to_stat[NUM_STATS_PER_GROUP] = {
 	CPUTIME_SYSTEM, CPUTIME_SOFTIRQ, CPUTIME_IRQ, CPUTIME_IDLE
 };
 
+static void print_hardirq_counts(void);
+
 static void update_cpustat(void)
 {
 	u8 i;
@@ -504,10 +513,150 @@ static void print_cpustat(void)
 			utilization[i][STATS_SYSTEM], utilization[i][STATS_SOFTIRQ],
 			utilization[i][STATS_HARDIRQ], utilization[i][STATS_IDLE]);
 	}
+	print_hardirq_counts();
+}
+
+#define HARDIRQ_PERCENT_THRESH		50
+#define NUM_HARDIRQ_REPORT		5
+static DECLARE_BITMAP(softlockup_hardirq_cpus, CONFIG_NR_CPUS);
+static DEFINE_PER_CPU(u32 *, hardirq_counts);
+
+static void find_counts_top(u32 *irq_counts, int *irq, u32 perirq_counts, int perirq_id, int range)
+{
+	unsigned int i, j;
+
+	for (i = 0; i < range; i++) {
+		if (perirq_counts > irq_counts[i]) {
+			for (j = range - 1; j > i; j--) {
+				irq_counts[j] = irq_counts[j - 1];
+				irq[j] = irq[j - 1];
+			}
+			irq_counts[j] = perirq_counts;
+			irq[j] = perirq_id;
+			break;
+		}
+	}
+}
+
+/*
+ * If the proportion of time spent handling irq exceeds HARDIRQ_PERCENT_THRESH%
+ * during sample_period, then it is necessary to record the counts of each irq.
+ */
+static inline bool need_record_irq_counts(int type)
+{
+	int tail = this_cpu_read(cpustat_tail);
+	u8 utilization;
+
+	if (--tail == -1)
+		tail = 4;
+	utilization = this_cpu_read(cpustat_utilization[tail][type]);
+	return utilization > HARDIRQ_PERCENT_THRESH;
 }
+
+/*
+ * Mark softlockup as potentially caused by hardirq
+ */
+static void set_potential_softlockup_hardirq(void)
+{
+	u32 i;
+	u32 *counts = __this_cpu_read(hardirq_counts);
+	int cpu = smp_processor_id();
+	struct irq_desc *desc;
+
+	if (!need_record_irq_counts(STATS_HARDIRQ))
+		return;
+
+	if (!test_bit(cpu, softlockup_hardirq_cpus)) {
+		counts = kmalloc_array(nr_irqs, sizeof(u32), GFP_ATOMIC);
+		if (!counts)
+			return;
+		for_each_irq_desc(i, desc) {
+			if (!desc)
+				continue;
+			counts[i] = desc->kstat_irqs ?
+				*this_cpu_ptr(desc->kstat_irqs) : 0;
+		}
+		__this_cpu_write(hardirq_counts, counts);
+		set_bit(cpu, softlockup_hardirq_cpus);
+	}
+}
+
+static void clear_potential_softlockup_hardirq(void)
+{
+	u32 *counts = __this_cpu_read(hardirq_counts);
+	int cpu = smp_processor_id();
+
+	if (test_bit(cpu, softlockup_hardirq_cpus)) {
+		kfree(counts);
+		counts = NULL;
+		__this_cpu_write(hardirq_counts, counts);
+		clear_bit(cpu, softlockup_hardirq_cpus);
+	}
+}
+
+/*
+ * Mark that softlockup may occur
+ */
+static void set_potential_softlockup(unsigned long now, unsigned long period_ts)
+{
+	if (time_after_eq(now, period_ts + get_softlockup_thresh() / 5))
+		set_potential_softlockup_hardirq();
+}
+
+static void clear_potential_softlockup(void)
+{
+	clear_potential_softlockup_hardirq();
+}
+
+static void print_hardirq_counts(void)
+{
+	u32 i;
+	struct irq_desc *desc;
+	u32 counts_diff;
+	u32 *counts = __this_cpu_read(hardirq_counts);
+	int cpu = smp_processor_id();
+	u32 hardirq_counts_top[NUM_HARDIRQ_REPORT] = {0, 0, 0, 0, 0};
+	int hardirq_top[NUM_HARDIRQ_REPORT] = {-1, -1, -1, -1, -1};
+
+	if (test_bit(cpu, softlockup_hardirq_cpus)) {
+		/* Find the top NUM_HARDIRQ_REPORT most frequent interrupts */
+		for_each_irq_desc(i, desc) {
+			if (!desc)
+				continue;
+			counts_diff = desc->kstat_irqs ?
+				*this_cpu_ptr(desc->kstat_irqs) - counts[i] : 0;
+			find_counts_top(hardirq_counts_top, hardirq_top,
+					counts_diff, i, NUM_HARDIRQ_REPORT);
+		}
+		/*
+		 * We do not want the "watchdog: " prefix on every line,
+		 * hence we use "printk" instead of "pr_crit".
+		 */
+		printk(KERN_CRIT "CPU#%d Detect HardIRQ Time exceeds %d%%. Most frequent HardIRQs:\n",
+			smp_processor_id(), HARDIRQ_PERCENT_THRESH);
+		for (i = 0; i < NUM_HARDIRQ_REPORT; i++) {
+			if (hardirq_top[i] == -1)
+				break;
+			desc = irq_to_desc(hardirq_top[i]);
+			if (desc && desc->action)
+				printk(KERN_CRIT "\t#%u: %-10u\tirq#%d(%s)\n",
+					i+1, hardirq_counts_top[i],
+					hardirq_top[i], desc->action->name);
+			else
+				printk(KERN_CRIT "\t#%u: %-10u\tirq#%d\n",
+					i+1, hardirq_counts_top[i],
+					hardirq_top[i]);
+		}
+		if (!need_record_irq_counts(STATS_HARDIRQ))
+			clear_potential_softlockup_hardirq();
+	}
+}
+
 #else
 static inline void update_cpustat(void) { }
 static inline void print_cpustat(void) { }
+static inline void set_potential_softlockup(unsigned long now, unsigned long period_ts) { }
+static inline void clear_potential_softlockup(void) { }
 #endif
 
 /* watchdog detector functions */
@@ -525,6 +674,7 @@ static DEFINE_PER_CPU(struct cpu_stop_work, softlockup_stop_work);
 static int softlockup_fn(void *data)
 {
 	update_touch_ts();
+	clear_potential_softlockup();
 	complete(this_cpu_ptr(&softlockup_completion));
 
 	return 0;
-- 
2.37.1 (Apple Git-137.1)