// SPDX-License-Identifier: GPL-2.0
/*
 *  NMI backtrace support
 *
 * Gratuitously copied from arch/x86/kernel/apic/hw_nmi.c by Russell King,
 * with the following header:
 *
 *  HW NMI watchdog support
 *
 *  started by Don Zickus, Copyright (C) 2010 Red Hat, Inc.
 *
 *  Arch specific calls to support NMI watchdog
 *
 *  Bits copied from original nmi.c file
 */
#include <linux/cpumask.h>
#include <linux/delay.h>
#include <linux/kprobes.h>
#include <linux/nmi.h>
#include <linux/cpu.h>
#include <linux/sched/debug.h>

#ifdef arch_trigger_cpumask_backtrace
/* For reliability, we're prepared to waste bits here. */
static DECLARE_BITMAP(backtrace_mask, NR_CPUS) __read_mostly;

/* "in progress" flag of arch_trigger_cpumask_backtrace */
static unsigned long backtrace_flag;

/*
 * When raise() is called it will be passed a pointer to the
 * backtrace_mask. Architectures that call nmi_cpu_backtrace()
 * directly from their raise() functions may rely on the mask
 * they are passed being updated as a side effect of this call.
 */
void nmi_trigger_cpumask_backtrace(const cpumask_t *mask,
                                   int exclude_cpu,
                                   void (*raise)(cpumask_t *mask))
{
        int i, this_cpu = get_cpu();

        if (test_and_set_bit(0, &backtrace_flag)) {
                /*
                 * If there is already a trigger_all_cpu_backtrace() in progress
                 * (backtrace_flag == 1), don't output double cpu dump infos.
                 */
                put_cpu();
                return;
        }

        cpumask_copy(to_cpumask(backtrace_mask), mask);
        if (exclude_cpu != -1)
                cpumask_clear_cpu(exclude_cpu, to_cpumask(backtrace_mask));

        /*
         * Don't try to send an NMI to this cpu; it may work on some
         * architectures, but on others it may not, and we'll get
         * information at least as useful just by doing a dump_stack() here.
         * Note that nmi_cpu_backtrace(NULL) will clear the cpu bit.
         */
        if (cpumask_test_cpu(this_cpu, to_cpumask(backtrace_mask)))
                nmi_cpu_backtrace(NULL);

        if (!cpumask_empty(to_cpumask(backtrace_mask))) {
                pr_info("Sending NMI from CPU %d to CPUs %*pbl:\n",
                        this_cpu, nr_cpumask_bits, to_cpumask(backtrace_mask));
                nmi_backtrace_stall_snap(to_cpumask(backtrace_mask));
                raise(to_cpumask(backtrace_mask));
        }

        /* Wait for up to 10 seconds for all CPUs to do the backtrace */
        for (i = 0; i < 10 * 1000; i++) {
                if (cpumask_empty(to_cpumask(backtrace_mask)))
                        break;
                mdelay(1);
                touch_softlockup_watchdog();
        }
        nmi_backtrace_stall_check(to_cpumask(backtrace_mask));

        /*
         * Force flush any remote buffers that might be stuck in IRQ context
         * and therefore could not run their irq_work.
         */
        printk_trigger_flush();

        clear_bit_unlock(0, &backtrace_flag);
        put_cpu();
}

// Dump stacks even for idle CPUs.
static bool backtrace_idle;
module_param(backtrace_idle, bool, 0644);

bool nmi_cpu_backtrace(struct pt_regs *regs)
{
        int cpu = smp_processor_id();
        unsigned long flags;

        if (cpumask_test_cpu(cpu, to_cpumask(backtrace_mask))) {
                /*
                 * Allow nested NMI backtraces while serializing
                 * against other CPUs.
                 */
                printk_cpu_sync_get_irqsave(flags);
                if (!READ_ONCE(backtrace_idle) && regs && cpu_in_idle(instruction_pointer(regs))) {
                        pr_warn("NMI backtrace for cpu %d skipped: idling at %pS\n",
                                cpu, (void *)instruction_pointer(regs));
                } else {
                        pr_warn("NMI backtrace for cpu %d\n", cpu);
                        if (regs)
                                show_regs(regs);
                        else
                                dump_stack();
                }
                printk_cpu_sync_put_irqrestore(flags);
                cpumask_clear_cpu(cpu, to_cpumask(backtrace_mask));
                return true;
        }

        return false;
}
NOKPROBE_SYMBOL(nmi_cpu_backtrace);
#endif