1 // SPDX-License-Identifier: GPL-2.0
3 * Detect hard lockups on a system using perf
5 * started by Don Zickus, Copyright (C) 2010 Red Hat, Inc.
7 * Note: Most of this code is borrowed heavily from the original softlockup
8 * detector, so thanks to Ingo for the initial implementation.
9 * Some chunks also taken from the old x86-specific nmi watchdog code, thanks
10 * to those contributors as well.
13 #define pr_fmt(fmt) "NMI watchdog: " fmt
15 #include <linux/nmi.h>
16 #include <linux/atomic.h>
17 #include <linux/module.h>
18 #include <linux/sched/debug.h>
20 #include <asm/irq_regs.h>
21 #include <linux/perf_event.h>
23 static DEFINE_PER_CPU(struct perf_event
*, watchdog_ev
);
24 static DEFINE_PER_CPU(struct perf_event
*, dead_event
);
25 static struct cpumask dead_events_mask
;
27 static atomic_t watchdog_cpus
= ATOMIC_INIT(0);
29 #ifdef CONFIG_HARDLOCKUP_CHECK_TIMESTAMP
30 static DEFINE_PER_CPU(ktime_t
, last_timestamp
);
31 static DEFINE_PER_CPU(unsigned int, nmi_rearmed
);
32 static ktime_t watchdog_hrtimer_sample_threshold __read_mostly
;
34 void watchdog_update_hrtimer_threshold(u64 period
)
37 * The hrtimer runs with a period of (watchdog_threshold * 2) / 5
39 * So it runs effectively with 2.5 times the rate of the NMI
40 * watchdog. That means the hrtimer should fire 2-3 times before
41 * the NMI watchdog expires. The NMI watchdog on x86 is based on
42 * unhalted CPU cycles, so if Turbo-Mode is enabled the CPU cycles
43 * might run way faster than expected and the NMI fires in a
44 * smaller period than the one deduced from the nominal CPU
45 * frequency. Depending on the Turbo-Mode factor this might be fast
46 * enough to get the NMI period smaller than the hrtimer watchdog
47 * period and trigger false positives.
49 * The sample threshold is used to check in the NMI handler whether
50 * the minimum time between two NMI samples has elapsed. That
51 * prevents false positives.
53 * Set this to 4/5 of the actual watchdog threshold period so the
54 * hrtimer is guaranteed to fire at least once within the real
57 watchdog_hrtimer_sample_threshold
= period
* 2;
60 static bool watchdog_check_timestamp(void)
62 ktime_t delta
, now
= ktime_get_mono_fast_ns();
64 delta
= now
- __this_cpu_read(last_timestamp
);
65 if (delta
< watchdog_hrtimer_sample_threshold
) {
67 * If ktime is jiffies based, a stalled timer would prevent
68 * jiffies from being incremented and the filter would look
69 * at a stale timestamp and never trigger.
71 if (__this_cpu_inc_return(nmi_rearmed
) < 10)
74 __this_cpu_write(nmi_rearmed
, 0);
75 __this_cpu_write(last_timestamp
, now
);
79 static inline bool watchdog_check_timestamp(void)
85 static struct perf_event_attr wd_hw_attr
= {
86 .type
= PERF_TYPE_HARDWARE
,
87 .config
= PERF_COUNT_HW_CPU_CYCLES
,
88 .size
= sizeof(struct perf_event_attr
),
93 /* Callback function for perf event subsystem */
94 static void watchdog_overflow_callback(struct perf_event
*event
,
95 struct perf_sample_data
*data
,
98 /* Ensure the watchdog never gets throttled */
99 event
->hw
.interrupts
= 0;
101 if (!watchdog_check_timestamp())
104 watchdog_hardlockup_check(smp_processor_id(), regs
);
107 static int hardlockup_detector_event_create(void)
110 struct perf_event_attr
*wd_attr
;
111 struct perf_event
*evt
;
114 * Preemption is not disabled because memory will be allocated.
115 * Ensure CPU-locality by calling this in per-CPU kthread.
117 WARN_ON(!is_percpu_thread());
118 cpu
= raw_smp_processor_id();
119 wd_attr
= &wd_hw_attr
;
120 wd_attr
->sample_period
= hw_nmi_get_sample_period(watchdog_thresh
);
122 /* Try to register using hardware perf events */
123 evt
= perf_event_create_kernel_counter(wd_attr
, cpu
, NULL
,
124 watchdog_overflow_callback
, NULL
);
126 pr_debug("Perf event create on CPU %d failed with %ld\n", cpu
,
130 this_cpu_write(watchdog_ev
, evt
);
135 * watchdog_hardlockup_enable - Enable the local event
137 * @cpu: The CPU to enable hard lockup on.
139 void watchdog_hardlockup_enable(unsigned int cpu
)
141 WARN_ON_ONCE(cpu
!= smp_processor_id());
143 if (hardlockup_detector_event_create())
146 /* use original value for check */
147 if (!atomic_fetch_inc(&watchdog_cpus
))
148 pr_info("Enabled. Permanently consumes one hw-PMU counter.\n");
150 perf_event_enable(this_cpu_read(watchdog_ev
));
154 * watchdog_hardlockup_disable - Disable the local event
156 * @cpu: The CPU to enable hard lockup on.
158 void watchdog_hardlockup_disable(unsigned int cpu
)
160 struct perf_event
*event
= this_cpu_read(watchdog_ev
);
162 WARN_ON_ONCE(cpu
!= smp_processor_id());
165 perf_event_disable(event
);
166 this_cpu_write(watchdog_ev
, NULL
);
167 this_cpu_write(dead_event
, event
);
168 cpumask_set_cpu(smp_processor_id(), &dead_events_mask
);
169 atomic_dec(&watchdog_cpus
);
174 * hardlockup_detector_perf_cleanup - Cleanup disabled events and destroy them
176 * Called from lockup_detector_cleanup(). Serialized by the caller.
178 void hardlockup_detector_perf_cleanup(void)
182 for_each_cpu(cpu
, &dead_events_mask
) {
183 struct perf_event
*event
= per_cpu(dead_event
, cpu
);
186 * Required because for_each_cpu() reports unconditionally
187 * CPU0 as set on UP kernels. Sigh.
190 perf_event_release_kernel(event
);
191 per_cpu(dead_event
, cpu
) = NULL
;
193 cpumask_clear(&dead_events_mask
);
197 * hardlockup_detector_perf_stop - Globally stop watchdog events
199 * Special interface for x86 to handle the perf HT bug.
201 void __init
hardlockup_detector_perf_stop(void)
205 lockdep_assert_cpus_held();
207 for_each_online_cpu(cpu
) {
208 struct perf_event
*event
= per_cpu(watchdog_ev
, cpu
);
211 perf_event_disable(event
);
216 * hardlockup_detector_perf_restart - Globally restart watchdog events
218 * Special interface for x86 to handle the perf HT bug.
220 void __init
hardlockup_detector_perf_restart(void)
224 lockdep_assert_cpus_held();
226 if (!(watchdog_enabled
& WATCHDOG_HARDLOCKUP_ENABLED
))
229 for_each_online_cpu(cpu
) {
230 struct perf_event
*event
= per_cpu(watchdog_ev
, cpu
);
233 perf_event_enable(event
);
237 bool __weak __init
arch_perf_nmi_is_available(void)
243 * watchdog_hardlockup_probe - Probe whether NMI event is available at all
245 int __init
watchdog_hardlockup_probe(void)
249 if (!arch_perf_nmi_is_available())
252 ret
= hardlockup_detector_event_create();
255 pr_info("Perf NMI watchdog permanently disabled\n");
257 perf_event_release_kernel(this_cpu_read(watchdog_ev
));
258 this_cpu_write(watchdog_ev
, NULL
);