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 */
36 void nmi_trigger_cpumask_backtrace(const cpumask_t *mask,
37 int exclude_cpu,
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_cpu != -1)
53 cpumask_clear_cpu(exclude_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 nmi_backtrace_stall_snap(to_cpumask(backtrace_mask));
68 raise(to_cpumask(backtrace_mask));
69 }
70
71 /* Wait for up to 10 seconds for all CPUs to do the backtrace */
72 for (i = 0; i < 10 * 1000; i++) {
73 if (cpumask_empty(to_cpumask(backtrace_mask)))
74 break;
75 mdelay(1);
76 touch_softlockup_watchdog();
77 }
78 nmi_backtrace_stall_check(to_cpumask(backtrace_mask));
79
80 /*
81 * Force flush any remote buffers that might be stuck in IRQ context
82 * and therefore could not run their irq_work.
83 */
84 printk_trigger_flush();
85
86 clear_bit_unlock(0, &backtrace_flag);
87 put_cpu();
88 }
89
90 // Dump stacks even for idle CPUs.
91 static bool backtrace_idle;
92 module_param(backtrace_idle, bool, 0644);
93
94 bool nmi_cpu_backtrace(struct pt_regs *regs)
95 {
96 int cpu = smp_processor_id();
97 unsigned long flags;
98
99 if (cpumask_test_cpu(cpu, to_cpumask(backtrace_mask))) {
100 /*
101 * Allow nested NMI backtraces while serializing
102 * against other CPUs.
103 */
104 printk_cpu_sync_get_irqsave(flags);
105 if (!READ_ONCE(backtrace_idle) && regs && cpu_in_idle(instruction_pointer(regs))) {
106 pr_warn("NMI backtrace for cpu %d skipped: idling at %pS\n",
107 cpu, (void *)instruction_pointer(regs));
108 } else {
109 pr_warn("NMI backtrace for cpu %d\n", cpu);
110 if (regs)
111 show_regs(regs);
112 else
113 dump_stack();
114 }
115 printk_cpu_sync_put_irqrestore(flags);
116 cpumask_clear_cpu(cpu, to_cpumask(backtrace_mask));
117 return true;
118 }
119
120 return false;
121 }
122 NOKPROBE_SYMBOL(nmi_cpu_backtrace);
123 #endif
124
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