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. */
25 static DECLARE_BITMAP(backtrace_mask, NR_CPUS) __read_mostly;
26
27 /* "in progress" flag of arch_trigger_cpumask_backtrace */
28 static 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 */
nmi_trigger_cpumask_backtrace(const cpumask_t * mask,bool exclude_self,void (* raise)(cpumask_t * mask))36 void 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.
89 static bool backtrace_idle;
90 module_param(backtrace_idle, bool, 0644);
91
nmi_cpu_backtrace(struct pt_regs * regs)92 bool 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 }
113 NOKPROBE_SYMBOL(nmi_cpu_backtrace);
114 #endif
115
