1 files changed, 470 insertions, 0 deletions
diff --git a/arch/powerpc/kernel/watchdog.c b/arch/powerpc/kernel/watchdog.c
new file mode 100644
index 000000000..75b2a6c4d
--- /dev/null
+++ b/arch/powerpc/kernel/watchdog.c
@@ -0,0 +1,470 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Watchdog support on powerpc systems.
+ *
+ * Copyright 2017, IBM Corporation.
+ *
+ * This uses code from arch/sparc/kernel/nmi.c and kernel/watchdog.c
+ */
+
+#define pr_fmt(fmt) "watchdog: " fmt
+
+#include <linux/kernel.h>
+#include <linux/param.h>
+#include <linux/init.h>
+#include <linux/percpu.h>
+#include <linux/cpu.h>
+#include <linux/nmi.h>
+#include <linux/module.h>
+#include <linux/export.h>
+#include <linux/kprobes.h>
+#include <linux/hardirq.h>
+#include <linux/reboot.h>
+#include <linux/slab.h>
+#include <linux/kdebug.h>
+#include <linux/sched/debug.h>
+#include <linux/delay.h>
+#include <linux/smp.h>
+
+#include <asm/paca.h>
+
+/*
+ * The powerpc watchdog ensures that each CPU is able to service timers.
+ * The watchdog sets up a simple timer on each CPU to run once per timer
+ * period, and updates a per-cpu timestamp and a "pending" cpumask. This is
+ * the heartbeat.
+ *
+ * Then there are two systems to check that the heartbeat is still running.
+ * The local soft-NMI, and the SMP checker.
+ *
+ * The soft-NMI checker can detect lockups on the local CPU. When interrupts
+ * are disabled with local_irq_disable(), platforms that use soft-masking
+ * can leave hardware interrupts enabled and handle them with a masked
+ * interrupt handler. The masked handler can send the timer interrupt to the
+ * watchdog's soft_nmi_interrupt(), which appears to Linux as an NMI
+ * interrupt, and can be used to detect CPUs stuck with IRQs disabled.
+ *
+ * The soft-NMI checker will compare the heartbeat timestamp for this CPU
+ * with the current time, and take action if the difference exceeds the
+ * watchdog threshold.
+ *
+ * The limitation of the soft-NMI watchdog is that it does not work when
+ * interrupts are hard disabled or otherwise not being serviced. This is
+ * solved by also having a SMP watchdog where all CPUs check all other
+ * CPUs heartbeat.
+ *
+ * The SMP checker can detect lockups on other CPUs. A gobal "pending"
+ * cpumask is kept, containing all CPUs which enable the watchdog. Each
+ * CPU clears their pending bit in their heartbeat timer. When the bitmask
+ * becomes empty, the last CPU to clear its pending bit updates a global
+ * timestamp and refills the pending bitmask.
+ *
+ * In the heartbeat timer, if any CPU notices that the global timestamp has
+ * not been updated for a period exceeding the watchdog threshold, then it
+ * means the CPU(s) with their bit still set in the pending mask have had
+ * their heartbeat stop, and action is taken.
+ *
+ * Some platforms implement true NMI IPIs, which can be used by the SMP
+ * watchdog to detect an unresponsive CPU and pull it out of its stuck
+ * state with the NMI IPI, to get crash/debug data from it. This way the
+ * SMP watchdog can detect hardware interrupts off lockups.
+ */
+
+static cpumask_t wd_cpus_enabled __read_mostly;
+
+static u64 wd_panic_timeout_tb __read_mostly; /* timebase ticks until panic */
+static u64 wd_smp_panic_timeout_tb __read_mostly; /* panic other CPUs */
+
+static u64 wd_timer_period_ms __read_mostly;  /* interval between heartbeat */
+
+static DEFINE_PER_CPU(struct hrtimer, wd_hrtimer);
+static DEFINE_PER_CPU(u64, wd_timer_tb);
+
+/* SMP checker bits */
+static unsigned long __wd_smp_lock;
+static cpumask_t wd_smp_cpus_pending;
+static cpumask_t wd_smp_cpus_stuck;
+static u64 wd_smp_last_reset_tb;
+
+static inline void wd_smp_lock(unsigned long *flags)
+{
+	/*
+	 * Avoid locking layers if possible.
+	 * This may be called from low level interrupt handlers at some
+	 * point in future.
+	 */
+	raw_local_irq_save(*flags);
+	hard_irq_disable(); /* Make it soft-NMI safe */
+	while (unlikely(test_and_set_bit_lock(0, &__wd_smp_lock))) {
+		raw_local_irq_restore(*flags);
+		spin_until_cond(!test_bit(0, &__wd_smp_lock));
+		raw_local_irq_save(*flags);
+		hard_irq_disable();
+	}
+}
+
+static inline void wd_smp_unlock(unsigned long *flags)
+{
+	clear_bit_unlock(0, &__wd_smp_lock);
+	raw_local_irq_restore(*flags);
+}
+
+static void wd_lockup_ipi(struct pt_regs *regs)
+{
+	int cpu = raw_smp_processor_id();
+	u64 tb = get_tb();
+
+	pr_emerg("CPU %d Hard LOCKUP\n", cpu);
+	pr_emerg("CPU %d TB:%lld, last heartbeat TB:%lld (%lldms ago)\n",
+		 cpu, tb, per_cpu(wd_timer_tb, cpu),
+		 tb_to_ns(tb - per_cpu(wd_timer_tb, cpu)) / 1000000);
+	print_modules();
+	print_irqtrace_events(current);
+	if (regs)
+		show_regs(regs);
+	else
+		dump_stack();
+
+	/* Do not panic from here because that can recurse into NMI IPI layer */
+}
+
+static void set_cpumask_stuck(const struct cpumask *cpumask, u64 tb)
+{
+	cpumask_or(&wd_smp_cpus_stuck, &wd_smp_cpus_stuck, cpumask);
+	cpumask_andnot(&wd_smp_cpus_pending, &wd_smp_cpus_pending, cpumask);
+	/*
+	 * See wd_smp_clear_cpu_pending()
+	 */
+	smp_mb();
+	if (cpumask_empty(&wd_smp_cpus_pending)) {
+		wd_smp_last_reset_tb = tb;
+		cpumask_andnot(&wd_smp_cpus_pending,
+				&wd_cpus_enabled,
+				&wd_smp_cpus_stuck);
+	}
+}
+static void set_cpu_stuck(int cpu, u64 tb)
+{
+	set_cpumask_stuck(cpumask_of(cpu), tb);
+}
+
+static void watchdog_smp_panic(int cpu, u64 tb)
+{
+	unsigned long flags;
+	int c;
+
+	wd_smp_lock(&flags);
+	/* Double check some things under lock */
+	if ((s64)(tb - wd_smp_last_reset_tb) < (s64)wd_smp_panic_timeout_tb)
+		goto out;
+	if (cpumask_test_cpu(cpu, &wd_smp_cpus_pending))
+		goto out;
+	if (cpumask_weight(&wd_smp_cpus_pending) == 0)
+		goto out;
+
+	pr_emerg("CPU %d detected hard LOCKUP on other CPUs %*pbl\n",
+		 cpu, cpumask_pr_args(&wd_smp_cpus_pending));
+	pr_emerg("CPU %d TB:%lld, last SMP heartbeat TB:%lld (%lldms ago)\n",
+		 cpu, tb, wd_smp_last_reset_tb,
+		 tb_to_ns(tb - wd_smp_last_reset_tb) / 1000000);
+
+	if (!sysctl_hardlockup_all_cpu_backtrace) {
+		/*
+		 * Try to trigger the stuck CPUs, unless we are going to
+		 * get a backtrace on all of them anyway.
+		 */
+		for_each_cpu(c, &wd_smp_cpus_pending) {
+			if (c == cpu)
+				continue;
+			smp_send_nmi_ipi(c, wd_lockup_ipi, 1000000);
+		}
+	}
+
+	/* Take the stuck CPUs out of the watch group */
+	set_cpumask_stuck(&wd_smp_cpus_pending, tb);
+
+	wd_smp_unlock(&flags);
+
+	printk_safe_flush();
+	/*
+	 * printk_safe_flush() seems to require another print
+	 * before anything actually goes out to console.
+	 */
+	if (sysctl_hardlockup_all_cpu_backtrace)
+		trigger_allbutself_cpu_backtrace();
+
+	if (hardlockup_panic)
+		nmi_panic(NULL, "Hard LOCKUP");
+
+	return;
+
+out:
+	wd_smp_unlock(&flags);
+}
+
+static void wd_smp_clear_cpu_pending(int cpu, u64 tb)
+{
+	if (!cpumask_test_cpu(cpu, &wd_smp_cpus_pending)) {
+		if (unlikely(cpumask_test_cpu(cpu, &wd_smp_cpus_stuck))) {
+			struct pt_regs *regs = get_irq_regs();
+			unsigned long flags;
+
+			wd_smp_lock(&flags);
+
+			pr_emerg("CPU %d became unstuck TB:%lld\n",
+				 cpu, tb);
+			print_irqtrace_events(current);
+			if (regs)
+				show_regs(regs);
+			else
+				dump_stack();
+
+			cpumask_clear_cpu(cpu, &wd_smp_cpus_stuck);
+			wd_smp_unlock(&flags);
+		} else {
+			/*
+			 * The last CPU to clear pending should have reset the
+			 * watchdog so we generally should not find it empty
+			 * here if our CPU was clear. However it could happen
+			 * due to a rare race with another CPU taking the
+			 * last CPU out of the mask concurrently.
+			 *
+			 * We can't add a warning for it. But just in case
+			 * there is a problem with the watchdog that is causing
+			 * the mask to not be reset, try to kick it along here.
+			 */
+			if (unlikely(cpumask_empty(&wd_smp_cpus_pending)))
+				goto none_pending;
+		}
+		return;
+	}
+
+	cpumask_clear_cpu(cpu, &wd_smp_cpus_pending);
+
+	/*
+	 * Order the store to clear pending with the load(s) to check all
+	 * words in the pending mask to check they are all empty. This orders
+	 * with the same barrier on another CPU. This prevents two CPUs
+	 * clearing the last 2 pending bits, but neither seeing the other's
+	 * store when checking if the mask is empty, and missing an empty
+	 * mask, which ends with a false positive.
+	 */
+	smp_mb();
+	if (cpumask_empty(&wd_smp_cpus_pending)) {
+		unsigned long flags;
+
+none_pending:
+		/*
+		 * Double check under lock because more than one CPU could see
+		 * a clear mask with the lockless check after clearing their
+		 * pending bits.
+		 */
+		wd_smp_lock(&flags);
+		if (cpumask_empty(&wd_smp_cpus_pending)) {
+			wd_smp_last_reset_tb = tb;
+			cpumask_andnot(&wd_smp_cpus_pending,
+					&wd_cpus_enabled,
+					&wd_smp_cpus_stuck);
+		}
+		wd_smp_unlock(&flags);
+	}
+}
+
+static void watchdog_timer_interrupt(int cpu)
+{
+	u64 tb = get_tb();
+
+	per_cpu(wd_timer_tb, cpu) = tb;
+
+	wd_smp_clear_cpu_pending(cpu, tb);
+
+	if ((s64)(tb - wd_smp_last_reset_tb) >= (s64)wd_smp_panic_timeout_tb)
+		watchdog_smp_panic(cpu, tb);
+}
+
+void soft_nmi_interrupt(struct pt_regs *regs)
+{
+	unsigned long flags;
+	int cpu = raw_smp_processor_id();
+	u64 tb;
+
+	if (!cpumask_test_cpu(cpu, &wd_cpus_enabled))
+		return;
+
+	nmi_enter();
+
+	__this_cpu_inc(irq_stat.soft_nmi_irqs);
+
+	tb = get_tb();
+	if (tb - per_cpu(wd_timer_tb, cpu) >= wd_panic_timeout_tb) {
+		wd_smp_lock(&flags);
+		if (cpumask_test_cpu(cpu, &wd_smp_cpus_stuck)) {
+			wd_smp_unlock(&flags);
+			goto out;
+		}
+		set_cpu_stuck(cpu, tb);
+
+		pr_emerg("CPU %d self-detected hard LOCKUP @ %pS\n",
+			 cpu, (void *)regs->nip);
+		pr_emerg("CPU %d TB:%lld, last heartbeat TB:%lld (%lldms ago)\n",
+			 cpu, tb, per_cpu(wd_timer_tb, cpu),
+			 tb_to_ns(tb - per_cpu(wd_timer_tb, cpu)) / 1000000);
+		print_modules();
+		print_irqtrace_events(current);
+		show_regs(regs);
+
+		wd_smp_unlock(&flags);
+
+		if (sysctl_hardlockup_all_cpu_backtrace)
+			trigger_allbutself_cpu_backtrace();
+
+		if (hardlockup_panic)
+			nmi_panic(regs, "Hard LOCKUP");
+	}
+	if (wd_panic_timeout_tb < 0x7fffffff)
+		mtspr(SPRN_DEC, wd_panic_timeout_tb);
+
+out:
+	nmi_exit();
+}
+
+static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
+{
+	int cpu = smp_processor_id();
+
+	if (!(watchdog_enabled & NMI_WATCHDOG_ENABLED))
+		return HRTIMER_NORESTART;
+
+	if (!cpumask_test_cpu(cpu, &watchdog_cpumask))
+		return HRTIMER_NORESTART;
+
+	watchdog_timer_interrupt(cpu);
+
+	hrtimer_forward_now(hrtimer, ms_to_ktime(wd_timer_period_ms));
+
+	return HRTIMER_RESTART;
+}
+
+void arch_touch_nmi_watchdog(void)
+{
+	unsigned long ticks = tb_ticks_per_usec * wd_timer_period_ms * 1000;
+	int cpu = smp_processor_id();
+	u64 tb;
+
+	if (!cpumask_test_cpu(cpu, &watchdog_cpumask))
+		return;
+
+	tb = get_tb();
+	if (tb - per_cpu(wd_timer_tb, cpu) >= ticks) {
+		per_cpu(wd_timer_tb, cpu) = tb;
+		wd_smp_clear_cpu_pending(cpu, tb);
+	}
+}
+EXPORT_SYMBOL(arch_touch_nmi_watchdog);
+
+static void start_watchdog(void *arg)
+{
+	struct hrtimer *hrtimer = this_cpu_ptr(&wd_hrtimer);
+	int cpu = smp_processor_id();
+	unsigned long flags;
+
+	if (cpumask_test_cpu(cpu, &wd_cpus_enabled)) {
+		WARN_ON(1);
+		return;
+	}
+
+	if (!(watchdog_enabled & NMI_WATCHDOG_ENABLED))
+		return;
+
+	if (!cpumask_test_cpu(cpu, &watchdog_cpumask))
+		return;
+
+	wd_smp_lock(&flags);
+	cpumask_set_cpu(cpu, &wd_cpus_enabled);
+	if (cpumask_weight(&wd_cpus_enabled) == 1) {
+		cpumask_set_cpu(cpu, &wd_smp_cpus_pending);
+		wd_smp_last_reset_tb = get_tb();
+	}
+	wd_smp_unlock(&flags);
+
+	*this_cpu_ptr(&wd_timer_tb) = get_tb();
+
+	hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
+	hrtimer->function = watchdog_timer_fn;
+	hrtimer_start(hrtimer, ms_to_ktime(wd_timer_period_ms),
+		      HRTIMER_MODE_REL_PINNED);
+}
+
+static int start_watchdog_on_cpu(unsigned int cpu)
+{
+	return smp_call_function_single(cpu, start_watchdog, NULL, true);
+}
+
+static void stop_watchdog(void *arg)
+{
+	struct hrtimer *hrtimer = this_cpu_ptr(&wd_hrtimer);
+	int cpu = smp_processor_id();
+	unsigned long flags;
+
+	if (!cpumask_test_cpu(cpu, &wd_cpus_enabled))
+		return; /* Can happen in CPU unplug case */
+
+	hrtimer_cancel(hrtimer);
+
+	wd_smp_lock(&flags);
+	cpumask_clear_cpu(cpu, &wd_cpus_enabled);
+	wd_smp_unlock(&flags);
+
+	wd_smp_clear_cpu_pending(cpu, get_tb());
+}
+
+static int stop_watchdog_on_cpu(unsigned int cpu)
+{
+	return smp_call_function_single(cpu, stop_watchdog, NULL, true);
+}
+
+static void watchdog_calc_timeouts(void)
+{
+	wd_panic_timeout_tb = watchdog_thresh * ppc_tb_freq;
+
+	/* Have the SMP detector trigger a bit later */
+	wd_smp_panic_timeout_tb = wd_panic_timeout_tb * 3 / 2;
+
+	/* 2/5 is the factor that the perf based detector uses */
+	wd_timer_period_ms = watchdog_thresh * 1000 * 2 / 5;
+}
+
+void watchdog_nmi_stop(void)
+{
+	int cpu;
+
+	for_each_cpu(cpu, &wd_cpus_enabled)
+		stop_watchdog_on_cpu(cpu);
+}
+
+void watchdog_nmi_start(void)
+{
+	int cpu;
+
+	watchdog_calc_timeouts();
+	for_each_cpu_and(cpu, cpu_online_mask, &watchdog_cpumask)
+		start_watchdog_on_cpu(cpu);
+}
+
+/*
+ * Invoked from core watchdog init.
+ */
+int __init watchdog_nmi_probe(void)
+{
+	int err;
+
+	err = cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN,
+					"powerpc/watchdog:online",
+					start_watchdog_on_cpu,
+					stop_watchdog_on_cpu);
+	if (err < 0) {
+		pr_warn("could not be initialized");
+		return err;
+	}
+	return 0;
+}