1 /*
2 * Detect hard lockups on a system
3 *
4 * started by Don Zickus, Copyright (C) 2010 Red Hat, Inc.
5 *
6 * Note: Most of this code is borrowed heavily from the original softlockup
7 * detector, so thanks to Ingo for the initial implementation.
8 * Some chunks also taken from the old x86-specific nmi watchdog code, thanks
9 * to those contributors as well.
10 */
11
12 #define pr_fmt(fmt) "NMI watchdog: " fmt
13
14 #include <linux/nmi.h>
15 #include <linux/module.h>
16 #include <asm/irq_regs.h>
17 #include <linux/perf_event.h>
18
19 static DEFINE_PER_CPU(bool, hard_watchdog_warn);
20 static DEFINE_PER_CPU(bool, watchdog_nmi_touch);
21 static DEFINE_PER_CPU(struct perf_event *, watchdog_ev);
22
23 /* boot commands */
24 /*
25 * Should we panic when a soft-lockup or hard-lockup occurs:
26 */
27 unsigned int __read_mostly hardlockup_panic =
28 CONFIG_BOOTPARAM_HARDLOCKUP_PANIC_VALUE;
29 static unsigned long hardlockup_allcpu_dumped;
30 /*
31 * We may not want to enable hard lockup detection by default in all cases,
32 * for example when running the kernel as a guest on a hypervisor. In these
33 * cases this function can be called to disable hard lockup detection. This
34 * function should only be executed once by the boot processor before the
35 * kernel command line parameters are parsed, because otherwise it is not
36 * possible to override this in hardlockup_panic_setup().
37 */
hardlockup_detector_disable(void)38 void hardlockup_detector_disable(void)
39 {
40 watchdog_enabled &= ~NMI_WATCHDOG_ENABLED;
41 }
42
hardlockup_panic_setup(char * str)43 static int __init hardlockup_panic_setup(char *str)
44 {
45 if (!strncmp(str, "panic", 5))
46 hardlockup_panic = 1;
47 else if (!strncmp(str, "nopanic", 7))
48 hardlockup_panic = 0;
49 else if (!strncmp(str, "0", 1))
50 watchdog_enabled &= ~NMI_WATCHDOG_ENABLED;
51 else if (!strncmp(str, "1", 1))
52 watchdog_enabled |= NMI_WATCHDOG_ENABLED;
53 return 1;
54 }
55 __setup("nmi_watchdog=", hardlockup_panic_setup);
56
touch_nmi_watchdog(void)57 void touch_nmi_watchdog(void)
58 {
59 /*
60 * Using __raw here because some code paths have
61 * preemption enabled. If preemption is enabled
62 * then interrupts should be enabled too, in which
63 * case we shouldn't have to worry about the watchdog
64 * going off.
65 */
66 raw_cpu_write(watchdog_nmi_touch, true);
67 touch_softlockup_watchdog();
68 }
69 EXPORT_SYMBOL(touch_nmi_watchdog);
70
71 static struct perf_event_attr wd_hw_attr = {
72 .type = PERF_TYPE_HARDWARE,
73 .config = PERF_COUNT_HW_CPU_CYCLES,
74 .size = sizeof(struct perf_event_attr),
75 .pinned = 1,
76 .disabled = 1,
77 };
78
79 /* Callback function for perf event subsystem */
watchdog_overflow_callback(struct perf_event * event,struct perf_sample_data * data,struct pt_regs * regs)80 static void watchdog_overflow_callback(struct perf_event *event,
81 struct perf_sample_data *data,
82 struct pt_regs *regs)
83 {
84 /* Ensure the watchdog never gets throttled */
85 event->hw.interrupts = 0;
86
87 if (atomic_read(&watchdog_park_in_progress) != 0)
88 return;
89
90 if (__this_cpu_read(watchdog_nmi_touch) == true) {
91 __this_cpu_write(watchdog_nmi_touch, false);
92 return;
93 }
94
95 /* check for a hardlockup
96 * This is done by making sure our timer interrupt
97 * is incrementing. The timer interrupt should have
98 * fired multiple times before we overflow'd. If it hasn't
99 * then this is a good indication the cpu is stuck
100 */
101 if (is_hardlockup()) {
102 int this_cpu = smp_processor_id();
103
104 /* only print hardlockups once */
105 if (__this_cpu_read(hard_watchdog_warn) == true)
106 return;
107
108 pr_emerg("Watchdog detected hard LOCKUP on cpu %d", this_cpu);
109 print_modules();
110 print_irqtrace_events(current);
111 if (regs)
112 show_regs(regs);
113 else
114 dump_stack();
115
116 /*
117 * Perform all-CPU dump only once to avoid multiple hardlockups
118 * generating interleaving traces
119 */
120 if (sysctl_hardlockup_all_cpu_backtrace &&
121 !test_and_set_bit(0, &hardlockup_allcpu_dumped))
122 trigger_allbutself_cpu_backtrace();
123
124 if (hardlockup_panic)
125 nmi_panic(regs, "Hard LOCKUP");
126
127 __this_cpu_write(hard_watchdog_warn, true);
128 return;
129 }
130
131 __this_cpu_write(hard_watchdog_warn, false);
132 return;
133 }
134
135 /*
136 * People like the simple clean cpu node info on boot.
137 * Reduce the watchdog noise by only printing messages
138 * that are different from what cpu0 displayed.
139 */
140 static unsigned long cpu0_err;
141
watchdog_nmi_enable(unsigned int cpu)142 int watchdog_nmi_enable(unsigned int cpu)
143 {
144 struct perf_event_attr *wd_attr;
145 struct perf_event *event = per_cpu(watchdog_ev, cpu);
146
147 /* nothing to do if the hard lockup detector is disabled */
148 if (!(watchdog_enabled & NMI_WATCHDOG_ENABLED))
149 goto out;
150
151 /* is it already setup and enabled? */
152 if (event && event->state > PERF_EVENT_STATE_OFF)
153 goto out;
154
155 /* it is setup but not enabled */
156 if (event != NULL)
157 goto out_enable;
158
159 wd_attr = &wd_hw_attr;
160 wd_attr->sample_period = hw_nmi_get_sample_period(watchdog_thresh);
161
162 /* Try to register using hardware perf events */
163 event = perf_event_create_kernel_counter(wd_attr, cpu, NULL, watchdog_overflow_callback, NULL);
164
165 /* save cpu0 error for future comparision */
166 if (cpu == 0 && IS_ERR(event))
167 cpu0_err = PTR_ERR(event);
168
169 if (!IS_ERR(event)) {
170 /* only print for cpu0 or different than cpu0 */
171 if (cpu == 0 || cpu0_err)
172 pr_info("enabled on all CPUs, permanently consumes one hw-PMU counter.\n");
173 goto out_save;
174 }
175
176 /*
177 * Disable the hard lockup detector if _any_ CPU fails to set up
178 * set up the hardware perf event. The watchdog() function checks
179 * the NMI_WATCHDOG_ENABLED bit periodically.
180 *
181 * The barriers are for syncing up watchdog_enabled across all the
182 * cpus, as clear_bit() does not use barriers.
183 */
184 smp_mb__before_atomic();
185 clear_bit(NMI_WATCHDOG_ENABLED_BIT, &watchdog_enabled);
186 smp_mb__after_atomic();
187
188 /* skip displaying the same error again */
189 if (cpu > 0 && (PTR_ERR(event) == cpu0_err))
190 return PTR_ERR(event);
191
192 /* vary the KERN level based on the returned errno */
193 if (PTR_ERR(event) == -EOPNOTSUPP)
194 pr_info("disabled (cpu%i): not supported (no LAPIC?)\n", cpu);
195 else if (PTR_ERR(event) == -ENOENT)
196 pr_warn("disabled (cpu%i): hardware events not enabled\n",
197 cpu);
198 else
199 pr_err("disabled (cpu%i): unable to create perf event: %ld\n",
200 cpu, PTR_ERR(event));
201
202 pr_info("Shutting down hard lockup detector on all cpus\n");
203
204 return PTR_ERR(event);
205
206 /* success path */
207 out_save:
208 per_cpu(watchdog_ev, cpu) = event;
209 out_enable:
210 perf_event_enable(per_cpu(watchdog_ev, cpu));
211 out:
212 return 0;
213 }
214
watchdog_nmi_disable(unsigned int cpu)215 void watchdog_nmi_disable(unsigned int cpu)
216 {
217 struct perf_event *event = per_cpu(watchdog_ev, cpu);
218
219 if (event) {
220 perf_event_disable(event);
221 per_cpu(watchdog_ev, cpu) = NULL;
222
223 /* should be in cleanup, but blocks oprofile */
224 perf_event_release_kernel(event);
225 }
226 if (cpu == 0) {
227 /* watchdog_nmi_enable() expects this to be zero initially. */
228 cpu0_err = 0;
229 }
230 }
231