xref: /kernel/linux/linux-5.10/lib/nmi_backtrace.c (revision 8c2ecf20) 
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
88// Dump stacks even for idle CPUs.
89static bool backtrace_idle;
90module_param(backtrace_idle, bool, 0644);
91
92bool nmi_cpu_backtrace(struct pt_regs *regs)
93{
94	int cpu = smp_processor_id();
95
96	if (cpumask_test_cpu(cpu, to_cpumask(backtrace_mask))) {
97		if (!READ_ONCE(backtrace_idle) && regs && cpu_in_idle(instruction_pointer(regs))) {
98			pr_warn("NMI backtrace for cpu %d skipped: idling at %pS\n",
99				cpu, (void *)instruction_pointer(regs));
100		} else {
101			pr_warn("NMI backtrace for cpu %d\n", cpu);
102			if (regs)
103				show_regs(regs);
104			else
105				dump_stack();
106		}
107		cpumask_clear_cpu(cpu, to_cpumask(backtrace_mask));
108		return true;
109	}
110
111	return false;
112}
113NOKPROBE_SYMBOL(nmi_cpu_backtrace);
114#endif
115