1 // SPDX-License-Identifier: GPL-2.0
2
3 #include <linux/cpu.h>
4 #include <linux/cpumask.h>
5 #include <linux/kernel.h>
6 #include <linux/nmi.h>
7 #include <linux/percpu-defs.h>
8
9 static cpumask_t __read_mostly watchdog_cpus;
10
11 static unsigned int watchdog_next_cpu(unsigned int cpu)
12 {
13 unsigned int next_cpu;
14
15 next_cpu = cpumask_next(cpu, &watchdog_cpus);
16 if (next_cpu >= nr_cpu_ids)
17 next_cpu = cpumask_first(&watchdog_cpus);
18
19 if (next_cpu == cpu)
20 return nr_cpu_ids;
21
22 return next_cpu;
23 }
24
25 int __init watchdog_hardlockup_probe(void)
26 {
27 return 0;
28 }
29
30 void watchdog_hardlockup_enable(unsigned int cpu)
31 {
32 unsigned int next_cpu;
33
34 /*
35 * The new CPU will be marked online before the hrtimer interrupt
36 * gets a chance to run on it. If another CPU tests for a
37 * hardlockup on the new CPU before it has run its the hrtimer
38 * interrupt, it will get a false positive. Touch the watchdog on
39 * the new CPU to delay the check for at least 3 sampling periods
40 * to guarantee one hrtimer has run on the new CPU.
41 */
42 watchdog_hardlockup_touch_cpu(cpu);
43
44 /*
45 * We are going to check the next CPU. Our watchdog_hrtimer
46 * need not be zero if the CPU has already been online earlier.
47 * Touch the watchdog on the next CPU to avoid false positive
48 * if we try to check it in less then 3 interrupts.
49 */
50 next_cpu = watchdog_next_cpu(cpu);
51 if (next_cpu < nr_cpu_ids)
52 watchdog_hardlockup_touch_cpu(next_cpu);
53
54 /*
55 * Makes sure that watchdog is touched on this CPU before
56 * other CPUs could see it in watchdog_cpus. The counter
57 * part is in watchdog_buddy_check_hardlockup().
58 */
59 smp_wmb();
60
61 cpumask_set_cpu(cpu, &watchdog_cpus);
62 }
63
64 void watchdog_hardlockup_disable(unsigned int cpu)
65 {
66 unsigned int next_cpu = watchdog_next_cpu(cpu);
67
68 /*
69 * Offlining this CPU will cause the CPU before this one to start
70 * checking the one after this one. If this CPU just finished checking
71 * the next CPU and updating hrtimer_interrupts_saved, and then the
72 * previous CPU checks it within one sample period, it will trigger a
73 * false positive. Touch the watchdog on the next CPU to prevent it.
74 */
75 if (next_cpu < nr_cpu_ids)
76 watchdog_hardlockup_touch_cpu(next_cpu);
77
78 /*
79 * Makes sure that watchdog is touched on the next CPU before
80 * this CPU disappear in watchdog_cpus. The counter part is in
81 * watchdog_buddy_check_hardlockup().
82 */
83 smp_wmb();
84
85 cpumask_clear_cpu(cpu, &watchdog_cpus);
86 }
87
88 void watchdog_buddy_check_hardlockup(int hrtimer_interrupts)
89 {
90 unsigned int next_cpu;
91
92 /*
93 * Test for hardlockups every 3 samples. The sample period is
94 * watchdog_thresh * 2 / 5, so 3 samples gets us back to slightly over
95 * watchdog_thresh (over by 20%).
96 */
97 if (hrtimer_interrupts % 3 != 0)
98 return;
99
100 /* check for a hardlockup on the next CPU */
101 next_cpu = watchdog_next_cpu(smp_processor_id());
102 if (next_cpu >= nr_cpu_ids)
103 return;
104
105 /*
106 * Make sure that the watchdog was touched on next CPU when
107 * watchdog_next_cpu() returned another one because of
108 * a change in watchdog_hardlockup_enable()/disable().
109 */
110 smp_rmb();
111
112 watchdog_hardlockup_check(next_cpu, NULL);
113 }
114
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