1/*
2 *  HW NMI watchdog support
3 *
4 *  started by Don Zickus, Copyright (C) 2010 Red Hat, Inc.
5 *
6 *  Arch specific calls to support NMI watchdog
7 *
8 *  Bits copied from original nmi.c file
9 *
10 */
11#include <asm/apic.h>
12#include <asm/nmi.h>
13
14#include <linux/cpumask.h>
15#include <linux/kdebug.h>
16#include <linux/notifier.h>
17#include <linux/kprobes.h>
18#include <linux/nmi.h>
19#include <linux/module.h>
20#include <linux/delay.h>
21#include <linux/seq_buf.h>
22
23#ifdef CONFIG_HARDLOCKUP_DETECTOR
24u64 hw_nmi_get_sample_period(int watchdog_thresh)
25{
26	return (u64)(cpu_khz) * 1000 * watchdog_thresh;
27}
28#endif
29
30#ifdef arch_trigger_all_cpu_backtrace
31/* For reliability, we're prepared to waste bits here. */
32static DECLARE_BITMAP(backtrace_mask, NR_CPUS) __read_mostly;
33static cpumask_t printtrace_mask;
34
35#define NMI_BUF_SIZE		4096
36
37struct nmi_seq_buf {
38	unsigned char		buffer[NMI_BUF_SIZE];
39	struct seq_buf		seq;
40};
41
42/* Safe printing in NMI context */
43static DEFINE_PER_CPU(struct nmi_seq_buf, nmi_print_seq);
44
45/* "in progress" flag of arch_trigger_all_cpu_backtrace */
46static unsigned long backtrace_flag;
47
48static void print_seq_line(struct nmi_seq_buf *s, int start, int end)
49{
50	const char *buf = s->buffer + start;
51
52	printk("%.*s", (end - start) + 1, buf);
53}
54
55void arch_trigger_all_cpu_backtrace(bool include_self)
56{
57	struct nmi_seq_buf *s;
58	int len;
59	int cpu;
60	int i;
61	int this_cpu = get_cpu();
62
63	if (test_and_set_bit(0, &backtrace_flag)) {
64		/*
65		 * If there is already a trigger_all_cpu_backtrace() in progress
66		 * (backtrace_flag == 1), don't output double cpu dump infos.
67		 */
68		put_cpu();
69		return;
70	}
71
72	cpumask_copy(to_cpumask(backtrace_mask), cpu_online_mask);
73	if (!include_self)
74		cpumask_clear_cpu(this_cpu, to_cpumask(backtrace_mask));
75
76	cpumask_copy(&printtrace_mask, to_cpumask(backtrace_mask));
77	/*
78	 * Set up per_cpu seq_buf buffers that the NMIs running on the other
79	 * CPUs will write to.
80	 */
81	for_each_cpu(cpu, to_cpumask(backtrace_mask)) {
82		s = &per_cpu(nmi_print_seq, cpu);
83		seq_buf_init(&s->seq, s->buffer, NMI_BUF_SIZE);
84	}
85
86	if (!cpumask_empty(to_cpumask(backtrace_mask))) {
87		pr_info("sending NMI to %s CPUs:\n",
88			(include_self ? "all" : "other"));
89		apic->send_IPI_mask(to_cpumask(backtrace_mask), NMI_VECTOR);
90	}
91
92	/* Wait for up to 10 seconds for all CPUs to do the backtrace */
93	for (i = 0; i < 10 * 1000; i++) {
94		if (cpumask_empty(to_cpumask(backtrace_mask)))
95			break;
96		mdelay(1);
97		touch_softlockup_watchdog();
98	}
99
100	/*
101	 * Now that all the NMIs have triggered, we can dump out their
102	 * back traces safely to the console.
103	 */
104	for_each_cpu(cpu, &printtrace_mask) {
105		int last_i = 0;
106
107		s = &per_cpu(nmi_print_seq, cpu);
108		len = seq_buf_used(&s->seq);
109		if (!len)
110			continue;
111
112		/* Print line by line. */
113		for (i = 0; i < len; i++) {
114			if (s->buffer[i] == '\n') {
115				print_seq_line(s, last_i, i);
116				last_i = i + 1;
117			}
118		}
119		/* Check if there was a partial line. */
120		if (last_i < len) {
121			print_seq_line(s, last_i, len - 1);
122			pr_cont("\n");
123		}
124	}
125
126	clear_bit(0, &backtrace_flag);
127	smp_mb__after_atomic();
128	put_cpu();
129}
130
131/*
132 * It is not safe to call printk() directly from NMI handlers.
133 * It may be fine if the NMI detected a lock up and we have no choice
134 * but to do so, but doing a NMI on all other CPUs to get a back trace
135 * can be done with a sysrq-l. We don't want that to lock up, which
136 * can happen if the NMI interrupts a printk in progress.
137 *
138 * Instead, we redirect the vprintk() to this nmi_vprintk() that writes
139 * the content into a per cpu seq_buf buffer. Then when the NMIs are
140 * all done, we can safely dump the contents of the seq_buf to a printk()
141 * from a non NMI context.
142 */
143static int nmi_vprintk(const char *fmt, va_list args)
144{
145	struct nmi_seq_buf *s = this_cpu_ptr(&nmi_print_seq);
146	unsigned int len = seq_buf_used(&s->seq);
147
148	seq_buf_vprintf(&s->seq, fmt, args);
149	return seq_buf_used(&s->seq) - len;
150}
151
152static int
153arch_trigger_all_cpu_backtrace_handler(unsigned int cmd, struct pt_regs *regs)
154{
155	int cpu;
156
157	cpu = smp_processor_id();
158
159	if (cpumask_test_cpu(cpu, to_cpumask(backtrace_mask))) {
160		printk_func_t printk_func_save = this_cpu_read(printk_func);
161
162		/* Replace printk to write into the NMI seq */
163		this_cpu_write(printk_func, nmi_vprintk);
164		printk(KERN_WARNING "NMI backtrace for cpu %d\n", cpu);
165		show_regs(regs);
166		this_cpu_write(printk_func, printk_func_save);
167
168		cpumask_clear_cpu(cpu, to_cpumask(backtrace_mask));
169		return NMI_HANDLED;
170	}
171
172	return NMI_DONE;
173}
174NOKPROBE_SYMBOL(arch_trigger_all_cpu_backtrace_handler);
175
176static int __init register_trigger_all_cpu_backtrace(void)
177{
178	register_nmi_handler(NMI_LOCAL, arch_trigger_all_cpu_backtrace_handler,
179				0, "arch_bt");
180	return 0;
181}
182early_initcall(register_trigger_all_cpu_backtrace);
183#endif
184