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
172