blob: 88d3d32e59236bc1127d88c781bc014d70920652 [file] [log] [blame]
Russell Kingb2c0b2c2014-09-03 23:57:13 +01001/*
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
46void nmi_trigger_all_cpu_backtrace(bool include_self,
47 void (*raise)(cpumask_t *mask))
48{
49 struct nmi_seq_buf *s;
50 int i, cpu, this_cpu = get_cpu();
51
52 if (test_and_set_bit(0, &backtrace_flag)) {
53 /*
54 * If there is already a trigger_all_cpu_backtrace() in progress
55 * (backtrace_flag == 1), don't output double cpu dump infos.
56 */
57 put_cpu();
58 return;
59 }
60
61 cpumask_copy(to_cpumask(backtrace_mask), cpu_online_mask);
62 if (!include_self)
63 cpumask_clear_cpu(this_cpu, to_cpumask(backtrace_mask));
64
65 cpumask_copy(&printtrace_mask, to_cpumask(backtrace_mask));
66
67 /*
68 * Set up per_cpu seq_buf buffers that the NMIs running on the other
69 * CPUs will write to.
70 */
71 for_each_cpu(cpu, to_cpumask(backtrace_mask)) {
72 s = &per_cpu(nmi_print_seq, cpu);
73 seq_buf_init(&s->seq, s->buffer, NMI_BUF_SIZE);
74 }
75
76 if (!cpumask_empty(to_cpumask(backtrace_mask))) {
77 pr_info("Sending NMI to %s CPUs:\n",
78 (include_self ? "all" : "other"));
79 raise(to_cpumask(backtrace_mask));
80 }
81
82 /* Wait for up to 10 seconds for all CPUs to do the backtrace */
83 for (i = 0; i < 10 * 1000; i++) {
84 if (cpumask_empty(to_cpumask(backtrace_mask)))
85 break;
86 mdelay(1);
87 touch_softlockup_watchdog();
88 }
89
90 /*
91 * Now that all the NMIs have triggered, we can dump out their
92 * back traces safely to the console.
93 */
94 for_each_cpu(cpu, &printtrace_mask) {
95 int len, last_i = 0;
96
97 s = &per_cpu(nmi_print_seq, cpu);
98 len = seq_buf_used(&s->seq);
99 if (!len)
100 continue;
101
102 /* Print line by line. */
103 for (i = 0; i < len; i++) {
104 if (s->buffer[i] == '\n') {
105 print_seq_line(s, last_i, i);
106 last_i = i + 1;
107 }
108 }
109 /* Check if there was a partial line. */
110 if (last_i < len) {
111 print_seq_line(s, last_i, len - 1);
112 pr_cont("\n");
113 }
114 }
115
116 clear_bit(0, &backtrace_flag);
117 smp_mb__after_atomic();
118 put_cpu();
119}
120
121/*
122 * It is not safe to call printk() directly from NMI handlers.
123 * It may be fine if the NMI detected a lock up and we have no choice
124 * but to do so, but doing a NMI on all other CPUs to get a back trace
125 * can be done with a sysrq-l. We don't want that to lock up, which
126 * can happen if the NMI interrupts a printk in progress.
127 *
128 * Instead, we redirect the vprintk() to this nmi_vprintk() that writes
129 * the content into a per cpu seq_buf buffer. Then when the NMIs are
130 * all done, we can safely dump the contents of the seq_buf to a printk()
131 * from a non NMI context.
132 */
133static int nmi_vprintk(const char *fmt, va_list args)
134{
135 struct nmi_seq_buf *s = this_cpu_ptr(&nmi_print_seq);
136 unsigned int len = seq_buf_used(&s->seq);
137
138 seq_buf_vprintf(&s->seq, fmt, args);
139 return seq_buf_used(&s->seq) - len;
140}
141
142bool nmi_cpu_backtrace(struct pt_regs *regs)
143{
144 int cpu = smp_processor_id();
145
146 if (cpumask_test_cpu(cpu, to_cpumask(backtrace_mask))) {
147 printk_func_t printk_func_save = this_cpu_read(printk_func);
148
149 /* Replace printk to write into the NMI seq */
150 this_cpu_write(printk_func, nmi_vprintk);
151 pr_warn("NMI backtrace for cpu %d\n", cpu);
152 show_regs(regs);
153 this_cpu_write(printk_func, printk_func_save);
154
155 cpumask_clear_cpu(cpu, to_cpumask(backtrace_mask));
156 return true;
157 }
158
159 return false;
160}
161NOKPROBE_SYMBOL(nmi_cpu_backtrace);
162#endif