11f423c90SDouglas Anderson // SPDX-License-Identifier: GPL-2.0 21f423c90SDouglas Anderson 31f423c90SDouglas Anderson #include <linux/cpu.h> 41f423c90SDouglas Anderson #include <linux/cpumask.h> 51f423c90SDouglas Anderson #include <linux/kernel.h> 61f423c90SDouglas Anderson #include <linux/nmi.h> 71f423c90SDouglas Anderson #include <linux/percpu-defs.h> 81f423c90SDouglas Anderson 91f423c90SDouglas Anderson static cpumask_t __read_mostly watchdog_cpus; 101f423c90SDouglas Anderson watchdog_next_cpu(unsigned int cpu)111f423c90SDouglas Andersonstatic unsigned int watchdog_next_cpu(unsigned int cpu) 121f423c90SDouglas Anderson { 131f423c90SDouglas Anderson unsigned int next_cpu; 141f423c90SDouglas Anderson 15813efda2SDouglas Anderson next_cpu = cpumask_next(cpu, &watchdog_cpus); 161f423c90SDouglas Anderson if (next_cpu >= nr_cpu_ids) 17813efda2SDouglas Anderson next_cpu = cpumask_first(&watchdog_cpus); 181f423c90SDouglas Anderson 191f423c90SDouglas Anderson if (next_cpu == cpu) 201f423c90SDouglas Anderson return nr_cpu_ids; 211f423c90SDouglas Anderson 221f423c90SDouglas Anderson return next_cpu; 231f423c90SDouglas Anderson } 241f423c90SDouglas Anderson watchdog_hardlockup_probe(void)251f423c90SDouglas Andersonint __init watchdog_hardlockup_probe(void) 261f423c90SDouglas Anderson { 271f423c90SDouglas Anderson return 0; 281f423c90SDouglas Anderson } 291f423c90SDouglas Anderson watchdog_hardlockup_enable(unsigned int cpu)301f423c90SDouglas Andersonvoid watchdog_hardlockup_enable(unsigned int cpu) 311f423c90SDouglas Anderson { 321f423c90SDouglas Anderson unsigned int next_cpu; 331f423c90SDouglas Anderson 341f423c90SDouglas Anderson /* 351f423c90SDouglas Anderson * The new CPU will be marked online before the hrtimer interrupt 361f423c90SDouglas Anderson * gets a chance to run on it. If another CPU tests for a 371f423c90SDouglas Anderson * hardlockup on the new CPU before it has run its the hrtimer 381f423c90SDouglas Anderson * interrupt, it will get a false positive. Touch the watchdog on 391f423c90SDouglas Anderson * the new CPU to delay the check for at least 3 sampling periods 401f423c90SDouglas Anderson * to guarantee one hrtimer has run on the new CPU. 411f423c90SDouglas Anderson */ 421f423c90SDouglas Anderson watchdog_hardlockup_touch_cpu(cpu); 431f423c90SDouglas Anderson 441f423c90SDouglas Anderson /* 451f423c90SDouglas Anderson * We are going to check the next CPU. Our watchdog_hrtimer 461f423c90SDouglas Anderson * need not be zero if the CPU has already been online earlier. 471f423c90SDouglas Anderson * Touch the watchdog on the next CPU to avoid false positive 481f423c90SDouglas Anderson * if we try to check it in less then 3 interrupts. 491f423c90SDouglas Anderson */ 501f423c90SDouglas Anderson next_cpu = watchdog_next_cpu(cpu); 511f423c90SDouglas Anderson if (next_cpu < nr_cpu_ids) 521f423c90SDouglas Anderson watchdog_hardlockup_touch_cpu(next_cpu); 531f423c90SDouglas Anderson 54*28168ecaSDouglas Anderson /* 55*28168ecaSDouglas Anderson * Makes sure that watchdog is touched on this CPU before 56*28168ecaSDouglas Anderson * other CPUs could see it in watchdog_cpus. The counter 57*28168ecaSDouglas Anderson * part is in watchdog_buddy_check_hardlockup(). 58*28168ecaSDouglas Anderson */ 59*28168ecaSDouglas Anderson smp_wmb(); 60*28168ecaSDouglas Anderson 611f423c90SDouglas Anderson cpumask_set_cpu(cpu, &watchdog_cpus); 621f423c90SDouglas Anderson } 631f423c90SDouglas Anderson watchdog_hardlockup_disable(unsigned int cpu)641f423c90SDouglas Andersonvoid watchdog_hardlockup_disable(unsigned int cpu) 651f423c90SDouglas Anderson { 661f423c90SDouglas Anderson unsigned int next_cpu = watchdog_next_cpu(cpu); 671f423c90SDouglas Anderson 681f423c90SDouglas Anderson /* 691f423c90SDouglas Anderson * Offlining this CPU will cause the CPU before this one to start 701f423c90SDouglas Anderson * checking the one after this one. If this CPU just finished checking 711f423c90SDouglas Anderson * the next CPU and updating hrtimer_interrupts_saved, and then the 721f423c90SDouglas Anderson * previous CPU checks it within one sample period, it will trigger a 731f423c90SDouglas Anderson * false positive. Touch the watchdog on the next CPU to prevent it. 741f423c90SDouglas Anderson */ 751f423c90SDouglas Anderson if (next_cpu < nr_cpu_ids) 761f423c90SDouglas Anderson watchdog_hardlockup_touch_cpu(next_cpu); 771f423c90SDouglas Anderson 78*28168ecaSDouglas Anderson /* 79*28168ecaSDouglas Anderson * Makes sure that watchdog is touched on the next CPU before 80*28168ecaSDouglas Anderson * this CPU disappear in watchdog_cpus. The counter part is in 81*28168ecaSDouglas Anderson * watchdog_buddy_check_hardlockup(). 82*28168ecaSDouglas Anderson */ 83*28168ecaSDouglas Anderson smp_wmb(); 84*28168ecaSDouglas Anderson 851f423c90SDouglas Anderson cpumask_clear_cpu(cpu, &watchdog_cpus); 861f423c90SDouglas Anderson } 871f423c90SDouglas Anderson watchdog_buddy_check_hardlockup(int hrtimer_interrupts)88d3b62aceSDouglas Andersonvoid watchdog_buddy_check_hardlockup(int hrtimer_interrupts) 891f423c90SDouglas Anderson { 901f423c90SDouglas Anderson unsigned int next_cpu; 911f423c90SDouglas Anderson 921f423c90SDouglas Anderson /* 931f423c90SDouglas Anderson * Test for hardlockups every 3 samples. The sample period is 941f423c90SDouglas Anderson * watchdog_thresh * 2 / 5, so 3 samples gets us back to slightly over 951f423c90SDouglas Anderson * watchdog_thresh (over by 20%). 961f423c90SDouglas Anderson */ 971f423c90SDouglas Anderson if (hrtimer_interrupts % 3 != 0) 981f423c90SDouglas Anderson return; 991f423c90SDouglas Anderson 1001f423c90SDouglas Anderson /* check for a hardlockup on the next CPU */ 1011f423c90SDouglas Anderson next_cpu = watchdog_next_cpu(smp_processor_id()); 1021f423c90SDouglas Anderson if (next_cpu >= nr_cpu_ids) 1031f423c90SDouglas Anderson return; 1041f423c90SDouglas Anderson 105*28168ecaSDouglas Anderson /* 106*28168ecaSDouglas Anderson * Make sure that the watchdog was touched on next CPU when 107*28168ecaSDouglas Anderson * watchdog_next_cpu() returned another one because of 108*28168ecaSDouglas Anderson * a change in watchdog_hardlockup_enable()/disable(). 109*28168ecaSDouglas Anderson */ 110*28168ecaSDouglas Anderson smp_rmb(); 111*28168ecaSDouglas Anderson 1121f423c90SDouglas Anderson watchdog_hardlockup_check(next_cpu, NULL); 1131f423c90SDouglas Anderson } 114