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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
1/*
2 * NMI backtrace support
3 *
4 * Gratuitously copied from arch/x86/kernel/apic/hw_nmi.c by Russell King,
5 * with the following header:
6 *
7 * HW NMI watchdog support
8 *
9 * started by Don Zickus, Copyright (C) 2010 Red Hat, Inc.
10 *
11 * Arch specific calls to support NMI watchdog
12 *
13 * Bits copied from original nmi.c file
14 */
15#include <linux/cpumask.h>
16#include <linux/delay.h>
17#include <linux/kprobes.h>
18#include <linux/nmi.h>
19#include <linux/seq_buf.h>
20
21#ifdef arch_trigger_all_cpu_backtrace
22/* For reliability, we're prepared to waste bits here. */
23static DECLARE_BITMAP(backtrace_mask, NR_CPUS) __read_mostly;
24static cpumask_t printtrace_mask;
25
26#define NMI_BUF_SIZE 4096
27
28struct nmi_seq_buf {
29 unsigned char buffer[NMI_BUF_SIZE];
30 struct seq_buf seq;
31};
32
33/* Safe printing in NMI context */
34static DEFINE_PER_CPU(struct nmi_seq_buf, nmi_print_seq);
35
36/* "in progress" flag of arch_trigger_all_cpu_backtrace */
37static unsigned long backtrace_flag;
38
39static void print_seq_line(struct nmi_seq_buf *s, int start, int end)
40{
41 const char *buf = s->buffer + start;
42
43 printk("%.*s", (end - start) + 1, buf);
44}
45
46/*
47 * When raise() is called it will be is passed a pointer to the
48 * backtrace_mask. Architectures that call nmi_cpu_backtrace()
49 * directly from their raise() functions may rely on the mask
50 * they are passed being updated as a side effect of this call.
51 */
52void nmi_trigger_all_cpu_backtrace(bool include_self,
53 void (*raise)(cpumask_t *mask))
54{
55 struct nmi_seq_buf *s;
56 int i, cpu, this_cpu = get_cpu();
57
58 if (test_and_set_bit(0, &backtrace_flag)) {
59 /*
60 * If there is already a trigger_all_cpu_backtrace() in progress
61 * (backtrace_flag == 1), don't output double cpu dump infos.
62 */
63 put_cpu();
64 return;
65 }
66
67 cpumask_copy(to_cpumask(backtrace_mask), cpu_online_mask);
68 if (!include_self)
69 cpumask_clear_cpu(this_cpu, to_cpumask(backtrace_mask));
70
71 cpumask_copy(&printtrace_mask, to_cpumask(backtrace_mask));
72
73 /*
74 * Set up per_cpu seq_buf buffers that the NMIs running on the other
75 * CPUs will write to.
76 */
77 for_each_cpu(cpu, to_cpumask(backtrace_mask)) {
78 s = &per_cpu(nmi_print_seq, cpu);
79 seq_buf_init(&s->seq, s->buffer, NMI_BUF_SIZE);
80 }
81
82 if (!cpumask_empty(to_cpumask(backtrace_mask))) {
83 pr_info("Sending NMI to %s CPUs:\n",
84 (include_self ? "all" : "other"));
85 raise(to_cpumask(backtrace_mask));
86 }
87
88 /* Wait for up to 10 seconds for all CPUs to do the backtrace */
89 for (i = 0; i < 10 * 1000; i++) {
90 if (cpumask_empty(to_cpumask(backtrace_mask)))
91 break;
92 mdelay(1);
93 touch_softlockup_watchdog();
94 }
95
96 /*
97 * Now that all the NMIs have triggered, we can dump out their
98 * back traces safely to the console.
99 */
100 for_each_cpu(cpu, &printtrace_mask) {
101 int len, last_i = 0;
102
103 s = &per_cpu(nmi_print_seq, cpu);
104 len = seq_buf_used(&s->seq);
105 if (!len)
106 continue;
107
108 /* Print line by line. */
109 for (i = 0; i < len; i++) {
110 if (s->buffer[i] == '\n') {
111 print_seq_line(s, last_i, i);
112 last_i = i + 1;
113 }
114 }
115 /* Check if there was a partial line. */
116 if (last_i < len) {
117 print_seq_line(s, last_i, len - 1);
118 pr_cont("\n");
119 }
120 }
121
122 clear_bit(0, &backtrace_flag);
123 smp_mb__after_atomic();
124 put_cpu();
125}
126
127/*
128 * It is not safe to call printk() directly from NMI handlers.
129 * It may be fine if the NMI detected a lock up and we have no choice
130 * but to do so, but doing a NMI on all other CPUs to get a back trace
131 * can be done with a sysrq-l. We don't want that to lock up, which
132 * can happen if the NMI interrupts a printk in progress.
133 *
134 * Instead, we redirect the vprintk() to this nmi_vprintk() that writes
135 * the content into a per cpu seq_buf buffer. Then when the NMIs are
136 * all done, we can safely dump the contents of the seq_buf to a printk()
137 * from a non NMI context.
138 */
139static int nmi_vprintk(const char *fmt, va_list args)
140{
141 struct nmi_seq_buf *s = this_cpu_ptr(&nmi_print_seq);
142 unsigned int len = seq_buf_used(&s->seq);
143
144 seq_buf_vprintf(&s->seq, fmt, args);
145 return seq_buf_used(&s->seq) - len;
146}
147
148bool nmi_cpu_backtrace(struct pt_regs *regs)
149{
150 int cpu = smp_processor_id();
151
152 if (cpumask_test_cpu(cpu, to_cpumask(backtrace_mask))) {
153 printk_func_t printk_func_save = this_cpu_read(printk_func);
154
155 /* Replace printk to write into the NMI seq */
156 this_cpu_write(printk_func, nmi_vprintk);
157 pr_warn("NMI backtrace for cpu %d\n", cpu);
158 if (regs)
159 show_regs(regs);
160 else
161 dump_stack();
162 this_cpu_write(printk_func, printk_func_save);
163
164 cpumask_clear_cpu(cpu, to_cpumask(backtrace_mask));
165 return true;
166 }
167
168 return false;
169}
170NOKPROBE_SYMBOL(nmi_cpu_backtrace);
171#endif