// 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 by 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 timer_list, wd_timer);
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)
{
        pr_emerg("CPU %d Hard LOCKUP\n", raw_smp_processor_id());
        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);
        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));

        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);
                }
                smp_flush_nmi_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))) {
                        unsigned long flags;

                        pr_emerg("CPU %d became unstuck\n", cpu);
                        wd_smp_lock(&flags);
                        cpumask_clear_cpu(cpu, &wd_smp_cpus_stuck);
                        wd_smp_unlock(&flags);
                }
                return;
        }
        cpumask_clear_cpu(cpu, &wd_smp_cpus_pending);
        if (cpumask_empty(&wd_smp_cpus_pending)) {
                unsigned long flags;

                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) {
                per_cpu(wd_timer_tb, cpu) = 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);
                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 void wd_timer_reset(unsigned int cpu, struct timer_list *t)
{
        t->expires = jiffies + msecs_to_jiffies(wd_timer_period_ms);
        if (wd_timer_period_ms > 1000)
                t->expires = __round_jiffies_up(t->expires, cpu);
        add_timer_on(t, cpu);
}

static void wd_timer_fn(struct timer_list *t)
{
        int cpu = smp_processor_id();

        watchdog_timer_interrupt(cpu);

        wd_timer_reset(cpu, t);
}

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 = 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_timer_on(unsigned int cpu)
{
        struct timer_list *t = per_cpu_ptr(&wd_timer, cpu);

        per_cpu(wd_timer_tb, cpu) = get_tb();

        timer_setup(t, wd_timer_fn, TIMER_PINNED);
        wd_timer_reset(cpu, t);
}

static void stop_watchdog_timer_on(unsigned int cpu)
{
        struct timer_list *t = per_cpu_ptr(&wd_timer, cpu);

        del_timer_sync(t);
}

static int start_wd_on_cpu(unsigned int cpu)
{
        unsigned long flags;

        if (cpumask_test_cpu(cpu, &wd_cpus_enabled)) {
                WARN_ON(1);
                return 0;
        }

        if (!(watchdog_enabled & NMI_WATCHDOG_ENABLED))
                return 0;

        if (!cpumask_test_cpu(cpu, &watchdog_cpumask))
                return 0;

        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);

        start_watchdog_timer_on(cpu);

        return 0;
}

static int stop_wd_on_cpu(unsigned int cpu)
{
        unsigned long flags;

        if (!cpumask_test_cpu(cpu, &wd_cpus_enabled))
                return 0; /* Can happen in CPU unplug case */

        stop_watchdog_timer_on(cpu);

        wd_smp_lock(&flags);
        cpumask_clear_cpu(cpu, &wd_cpus_enabled);
        wd_smp_unlock(&flags);

        wd_smp_clear_cpu_pending(cpu, get_tb());

        return 0;
}

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_wd_on_cpu(cpu);
}

void watchdog_nmi_start(void)
{
        int cpu;

        watchdog_calc_timeouts();
        for_each_cpu_and(cpu, cpu_online_mask, &watchdog_cpumask)
                start_wd_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_wd_on_cpu, stop_wd_on_cpu);
        if (err < 0) {
                pr_warn("could not be initialized");
                return err;
        }
        return 0;
}