watchdog_hld.c

 1// SPDX-License-Identifier: GPL-2.0
 2#include <linux/nmi.h>
 3#include <linux/cpufreq.h>
 4#include <linux/perf/arm_pmu.h>
 5
 6/*
 7 * Safe maximum CPU frequency in case a particular platform doesn't implement
 8 * cpufreq driver. Although, architecture doesn't put any restrictions on
 9 * maximum frequency but 5 GHz seems to be safe maximum given the available
10 * Arm CPUs in the market which are clocked much less than 5 GHz. On the other
11 * hand, we can't make it much higher as it would lead to a large hard-lockup
12 * detection timeout on parts which are running slower (eg. 1GHz on
13 * Developerbox) and doesn't possess a cpufreq driver.
14 */
15#define SAFE_MAX_CPU_FREQ	5000000000UL // 5 GHz
16u64 hw_nmi_get_sample_period(int watchdog_thresh)
17{
18	unsigned int cpu = smp_processor_id();
19	unsigned long max_cpu_freq;
20
21	max_cpu_freq = cpufreq_get_hw_max_freq(cpu) * 1000UL;
22	if (!max_cpu_freq)
23		max_cpu_freq = SAFE_MAX_CPU_FREQ;
24
25	return (u64)max_cpu_freq * watchdog_thresh;
26}
27
28bool __init arch_perf_nmi_is_available(void)
29{
30	/*
31	 * hardlockup_detector_perf_init() will success even if Pseudo-NMI turns off,
32	 * however, the pmu interrupts will act like a normal interrupt instead of
33	 * NMI and the hardlockup detector would be broken.
34	 */
35	return arm_pmu_irq_is_nmi();
36}
37
38static int watchdog_perf_update_period(void *data)
39{
40	int cpu = smp_processor_id();
41	u64 max_cpu_freq, new_period;
42
43	max_cpu_freq = cpufreq_get_hw_max_freq(cpu) * 1000UL;
44	if (!max_cpu_freq)
45		return 0;
46
47	new_period = watchdog_thresh * max_cpu_freq;
48	hardlockup_detector_perf_adjust_period(new_period);
49
50	return 0;
51}
52
53static int watchdog_freq_notifier_callback(struct notifier_block *nb,
54					   unsigned long val, void *data)
55{
56	struct cpufreq_policy *policy = data;
57	int cpu;
58
59	if (val != CPUFREQ_CREATE_POLICY)
60		return NOTIFY_DONE;
61
62	/*
63	 * Let each online CPU related to the policy update the period by their
64	 * own. This will serialize with the framework on start/stop the lockup
65	 * detector (softlockup_{start,stop}_all) and avoid potential race
66	 * condition. Otherwise we may have below theoretical race condition:
67	 * (core 0/1 share the same policy)
68	 * [core 0]                      [core 1]
69	 *                               hardlockup_detector_event_create()
70	 *                                 hw_nmi_get_sample_period()
71	 * (cpufreq registered, notifier callback invoked)
72	 * watchdog_freq_notifier_callback()
73	 *   watchdog_perf_update_period()
74	 *   (since core 1's event's not yet created,
75	 *    the period is not set)
76	 *                                 perf_event_create_kernel_counter()
77	 *                                 (event's period is SAFE_MAX_CPU_FREQ)
78	 */
79	for_each_cpu(cpu, policy->cpus)
80		smp_call_on_cpu(cpu, watchdog_perf_update_period, NULL, false);
81
82	return NOTIFY_DONE;
83}
84
85static struct notifier_block watchdog_freq_notifier = {
86	.notifier_call = watchdog_freq_notifier_callback,
87};
88
89static int __init init_watchdog_freq_notifier(void)
90{
91	return cpufreq_register_notifier(&watchdog_freq_notifier,
92					 CPUFREQ_POLICY_NOTIFIER);
93}
94core_initcall(init_watchdog_freq_notifier);