1// SPDX-License-Identifier: GPL-2.0
  2/*
  3 *  NMI backtrace support
  4 *
  5 * Gratuitously copied from arch/x86/kernel/apic/hw_nmi.c by Russell King,
  6 * with the following header:
  7 *
  8 *  HW NMI watchdog support
  9 *
 10 *  started by Don Zickus, Copyright (C) 2010 Red Hat, Inc.
 11 *
 12 *  Arch specific calls to support NMI watchdog
 13 *
 14 *  Bits copied from original nmi.c file
 15 */
 16#include <linux/cpumask.h>
 17#include <linux/delay.h>
 18#include <linux/kprobes.h>
 19#include <linux/nmi.h>
 20#include <linux/cpu.h>
 21#include <linux/sched/debug.h>
 22
 23#ifdef arch_trigger_cpumask_backtrace
 24/* For reliability, we're prepared to waste bits here. */
 25static DECLARE_BITMAP(backtrace_mask, NR_CPUS) __read_mostly;
 26
 27/* "in progress" flag of arch_trigger_cpumask_backtrace */
 28static unsigned long backtrace_flag;
 29
 30/*
 31 * When raise() is called it will be passed a pointer to the
 32 * backtrace_mask. Architectures that call nmi_cpu_backtrace()
 33 * directly from their raise() functions may rely on the mask
 34 * they are passed being updated as a side effect of this call.
 35 */
 36void nmi_trigger_cpumask_backtrace(const cpumask_t *mask,
 37				   bool exclude_self,
 38				   void (*raise)(cpumask_t *mask))
 39{
 40	int i, this_cpu = get_cpu();
 41
 42	if (test_and_set_bit(0, &backtrace_flag)) {
 43		/*
 44		 * If there is already a trigger_all_cpu_backtrace() in progress
 45		 * (backtrace_flag == 1), don't output double cpu dump infos.
 46		 */
 47		put_cpu();
 48		return;
 49	}
 50
 51	cpumask_copy(to_cpumask(backtrace_mask), mask);
 52	if (exclude_self)
 53		cpumask_clear_cpu(this_cpu, to_cpumask(backtrace_mask));
 54
 55	/*
 56	 * Don't try to send an NMI to this cpu; it may work on some
 57	 * architectures, but on others it may not, and we'll get
 58	 * information at least as useful just by doing a dump_stack() here.
 59	 * Note that nmi_cpu_backtrace(NULL) will clear the cpu bit.
 60	 */
 61	if (cpumask_test_cpu(this_cpu, to_cpumask(backtrace_mask)))
 62		nmi_cpu_backtrace(NULL);
 63
 64	if (!cpumask_empty(to_cpumask(backtrace_mask))) {
 65		pr_info("Sending NMI from CPU %d to CPUs %*pbl:\n",
 66			this_cpu, nr_cpumask_bits, to_cpumask(backtrace_mask));
 67		raise(to_cpumask(backtrace_mask));
 68	}
 69
 70	/* Wait for up to 10 seconds for all CPUs to do the backtrace */
 71	for (i = 0; i < 10 * 1000; i++) {
 72		if (cpumask_empty(to_cpumask(backtrace_mask)))
 73			break;
 74		mdelay(1);
 75		touch_softlockup_watchdog();
 76	}
 77
 78	/*
 79	 * Force flush any remote buffers that might be stuck in IRQ context
 80	 * and therefore could not run their irq_work.
 81	 */
 82	printk_safe_flush();
 83
 84	clear_bit_unlock(0, &backtrace_flag);
 85	put_cpu();
 86}
 87
 88bool nmi_cpu_backtrace(struct pt_regs *regs)
 89{
 90	int cpu = smp_processor_id();
 91
 92	if (cpumask_test_cpu(cpu, to_cpumask(backtrace_mask))) {
 93		if (regs && cpu_in_idle(instruction_pointer(regs))) {
 94			pr_warn("NMI backtrace for cpu %d skipped: idling at %pS\n",
 95				cpu, (void *)instruction_pointer(regs));
 96		} else {
 97			pr_warn("NMI backtrace for cpu %d\n", cpu);
 98			if (regs)
 99				show_regs(regs);
100			else
101				dump_stack();
102		}
103		cpumask_clear_cpu(cpu, to_cpumask(backtrace_mask));
104		return true;
105	}
106
107	return false;
108}
109NOKPROBE_SYMBOL(nmi_cpu_backtrace);
110#endif