diff options
Diffstat (limited to 'kernel/watchdog.c')
| -rw-r--r-- | kernel/watchdog.c | 890 |
1 files changed, 890 insertions, 0 deletions
diff --git a/kernel/watchdog.c b/kernel/watchdog.c new file mode 100644 index 000000000..581a68a04 --- /dev/null +++ b/kernel/watchdog.c @@ -0,0 +1,890 @@ +/* + * Detect hard and soft lockups on a system + * + * started by Don Zickus, Copyright (C) 2010 Red Hat, Inc. + * + * Note: Most of this code is borrowed heavily from the original softlockup + * detector, so thanks to Ingo for the initial implementation. + * Some chunks also taken from the old x86-specific nmi watchdog code, thanks + * to those contributors as well. + */ + +#define pr_fmt(fmt) "NMI watchdog: " fmt + +#include <linux/mm.h> +#include <linux/cpu.h> +#include <linux/nmi.h> +#include <linux/init.h> +#include <linux/module.h> +#include <linux/sysctl.h> +#include <linux/smpboot.h> +#include <linux/sched/rt.h> + +#include <asm/irq_regs.h> +#include <linux/kvm_para.h> +#include <linux/perf_event.h> + +/* + * The run state of the lockup detectors is controlled by the content of the + * 'watchdog_enabled' variable. Each lockup detector has its dedicated bit - + * bit 0 for the hard lockup detector and bit 1 for the soft lockup detector. + * + * 'watchdog_user_enabled', 'nmi_watchdog_enabled' and 'soft_watchdog_enabled' + * are variables that are only used as an 'interface' between the parameters + * in /proc/sys/kernel and the internal state bits in 'watchdog_enabled'. The + * 'watchdog_thresh' variable is handled differently because its value is not + * boolean, and the lockup detectors are 'suspended' while 'watchdog_thresh' + * is equal zero. + */ +#define NMI_WATCHDOG_ENABLED_BIT 0 +#define SOFT_WATCHDOG_ENABLED_BIT 1 +#define NMI_WATCHDOG_ENABLED (1 << NMI_WATCHDOG_ENABLED_BIT) +#define SOFT_WATCHDOG_ENABLED (1 << SOFT_WATCHDOG_ENABLED_BIT) + +static DEFINE_MUTEX(watchdog_proc_mutex); + +#ifdef CONFIG_HARDLOCKUP_DETECTOR +static unsigned long __read_mostly watchdog_enabled = SOFT_WATCHDOG_ENABLED|NMI_WATCHDOG_ENABLED; +#else +static unsigned long __read_mostly watchdog_enabled = SOFT_WATCHDOG_ENABLED; +#endif +int __read_mostly nmi_watchdog_enabled; +int __read_mostly soft_watchdog_enabled; +int __read_mostly watchdog_user_enabled; +int __read_mostly watchdog_thresh = 10; + +#ifdef CONFIG_SMP +int __read_mostly sysctl_softlockup_all_cpu_backtrace; +#else +#define sysctl_softlockup_all_cpu_backtrace 0 +#endif + +static int __read_mostly watchdog_running; +static u64 __read_mostly sample_period; + +static DEFINE_PER_CPU(unsigned long, watchdog_touch_ts); +static DEFINE_PER_CPU(struct task_struct *, softlockup_watchdog); +static DEFINE_PER_CPU(struct hrtimer, watchdog_hrtimer); +static DEFINE_PER_CPU(bool, softlockup_touch_sync); +static DEFINE_PER_CPU(bool, soft_watchdog_warn); +static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts); +static DEFINE_PER_CPU(unsigned long, soft_lockup_hrtimer_cnt); +static DEFINE_PER_CPU(struct task_struct *, softlockup_task_ptr_saved); +#ifdef CONFIG_HARDLOCKUP_DETECTOR +static DEFINE_PER_CPU(bool, hard_watchdog_warn); +static DEFINE_PER_CPU(bool, watchdog_nmi_touch); +static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts_saved); +static DEFINE_PER_CPU(struct perf_event *, watchdog_ev); +#endif +static unsigned long soft_lockup_nmi_warn; + +/* boot commands */ +/* + * Should we panic when a soft-lockup or hard-lockup occurs: + */ +#ifdef CONFIG_HARDLOCKUP_DETECTOR +static int hardlockup_panic = + CONFIG_BOOTPARAM_HARDLOCKUP_PANIC_VALUE; +/* + * We may not want to enable hard lockup detection by default in all cases, + * for example when running the kernel as a guest on a hypervisor. In these + * cases this function can be called to disable hard lockup detection. This + * function should only be executed once by the boot processor before the + * kernel command line parameters are parsed, because otherwise it is not + * possible to override this in hardlockup_panic_setup(). + */ +void hardlockup_detector_disable(void) +{ + watchdog_enabled &= ~NMI_WATCHDOG_ENABLED; +} + +static int __init hardlockup_panic_setup(char *str) +{ + if (!strncmp(str, "panic", 5)) + hardlockup_panic = 1; + else if (!strncmp(str, "nopanic", 7)) + hardlockup_panic = 0; + else if (!strncmp(str, "0", 1)) + watchdog_enabled &= ~NMI_WATCHDOG_ENABLED; + else if (!strncmp(str, "1", 1)) + watchdog_enabled |= NMI_WATCHDOG_ENABLED; + return 1; +} +__setup("nmi_watchdog=", hardlockup_panic_setup); +#endif + +unsigned int __read_mostly softlockup_panic = + CONFIG_BOOTPARAM_SOFTLOCKUP_PANIC_VALUE; + +static int __init softlockup_panic_setup(char *str) +{ + softlockup_panic = simple_strtoul(str, NULL, 0); + + return 1; +} +__setup("softlockup_panic=", softlockup_panic_setup); + +static int __init nowatchdog_setup(char *str) +{ + watchdog_enabled = 0; + return 1; +} +__setup("nowatchdog", nowatchdog_setup); + +static int __init nosoftlockup_setup(char *str) +{ + watchdog_enabled &= ~SOFT_WATCHDOG_ENABLED; + return 1; +} +__setup("nosoftlockup", nosoftlockup_setup); + +#ifdef CONFIG_SMP +static int __init softlockup_all_cpu_backtrace_setup(char *str) +{ + sysctl_softlockup_all_cpu_backtrace = + !!simple_strtol(str, NULL, 0); + return 1; +} +__setup("softlockup_all_cpu_backtrace=", softlockup_all_cpu_backtrace_setup); +#endif + +/* + * Hard-lockup warnings should be triggered after just a few seconds. Soft- + * lockups can have false positives under extreme conditions. So we generally + * want a higher threshold for soft lockups than for hard lockups. So we couple + * the thresholds with a factor: we make the soft threshold twice the amount of + * time the hard threshold is. + */ +static int get_softlockup_thresh(void) +{ + return watchdog_thresh * 2; +} + +/* + * Returns seconds, approximately. We don't need nanosecond + * resolution, and we don't need to waste time with a big divide when + * 2^30ns == 1.074s. + */ +static unsigned long get_timestamp(void) +{ + return running_clock() >> 30LL; /* 2^30 ~= 10^9 */ +} + +static void set_sample_period(void) +{ + /* + * convert watchdog_thresh from seconds to ns + * the divide by 5 is to give hrtimer several chances (two + * or three with the current relation between the soft + * and hard thresholds) to increment before the + * hardlockup detector generates a warning + */ + sample_period = get_softlockup_thresh() * ((u64)NSEC_PER_SEC / 5); +} + +/* Commands for resetting the watchdog */ +static void __touch_watchdog(void) +{ + __this_cpu_write(watchdog_touch_ts, get_timestamp()); +} + +void touch_softlockup_watchdog(void) +{ + /* + * Preemption can be enabled. It doesn't matter which CPU's timestamp + * gets zeroed here, so use the raw_ operation. + */ + raw_cpu_write(watchdog_touch_ts, 0); +} +EXPORT_SYMBOL(touch_softlockup_watchdog); + +void touch_all_softlockup_watchdogs(void) +{ + int cpu; + + /* + * this is done lockless + * do we care if a 0 races with a timestamp? + * all it means is the softlock check starts one cycle later + */ + for_each_online_cpu(cpu) + per_cpu(watchdog_touch_ts, cpu) = 0; +} + +#ifdef CONFIG_HARDLOCKUP_DETECTOR +void touch_nmi_watchdog(void) +{ + /* + * Using __raw here because some code paths have + * preemption enabled. If preemption is enabled + * then interrupts should be enabled too, in which + * case we shouldn't have to worry about the watchdog + * going off. + */ + raw_cpu_write(watchdog_nmi_touch, true); + touch_softlockup_watchdog(); +} +EXPORT_SYMBOL(touch_nmi_watchdog); + +#endif + +void touch_softlockup_watchdog_sync(void) +{ + __this_cpu_write(softlockup_touch_sync, true); + __this_cpu_write(watchdog_touch_ts, 0); +} + +#ifdef CONFIG_HARDLOCKUP_DETECTOR +/* watchdog detector functions */ +static int is_hardlockup(void) +{ + unsigned long hrint = __this_cpu_read(hrtimer_interrupts); + + if (__this_cpu_read(hrtimer_interrupts_saved) == hrint) + return 1; + + __this_cpu_write(hrtimer_interrupts_saved, hrint); + return 0; +} +#endif + +static int is_softlockup(unsigned long touch_ts) +{ + unsigned long now = get_timestamp(); + + if (watchdog_enabled & SOFT_WATCHDOG_ENABLED) { + /* Warn about unreasonable delays. */ + if (time_after(now, touch_ts + get_softlockup_thresh())) + return now - touch_ts; + } + return 0; +} + +#ifdef CONFIG_HARDLOCKUP_DETECTOR + +static struct perf_event_attr wd_hw_attr = { + .type = PERF_TYPE_HARDWARE, + .config = PERF_COUNT_HW_CPU_CYCLES, + .size = sizeof(struct perf_event_attr), + .pinned = 1, + .disabled = 1, +}; + +/* Callback function for perf event subsystem */ +static void watchdog_overflow_callback(struct perf_event *event, + struct perf_sample_data *data, + struct pt_regs *regs) +{ + /* Ensure the watchdog never gets throttled */ + event->hw.interrupts = 0; + + if (__this_cpu_read(watchdog_nmi_touch) == true) { + __this_cpu_write(watchdog_nmi_touch, false); + return; + } + + /* check for a hardlockup + * This is done by making sure our timer interrupt + * is incrementing. The timer interrupt should have + * fired multiple times before we overflow'd. If it hasn't + * then this is a good indication the cpu is stuck + */ + if (is_hardlockup()) { + int this_cpu = smp_processor_id(); + + /* only print hardlockups once */ + if (__this_cpu_read(hard_watchdog_warn) == true) + return; + + if (hardlockup_panic) + panic("Watchdog detected hard LOCKUP on cpu %d", + this_cpu); + else + WARN(1, "Watchdog detected hard LOCKUP on cpu %d", + this_cpu); + + __this_cpu_write(hard_watchdog_warn, true); + return; + } + + __this_cpu_write(hard_watchdog_warn, false); + return; +} +#endif /* CONFIG_HARDLOCKUP_DETECTOR */ + +static void watchdog_interrupt_count(void) +{ + __this_cpu_inc(hrtimer_interrupts); +} + +static int watchdog_nmi_enable(unsigned int cpu); +static void watchdog_nmi_disable(unsigned int cpu); + +/* watchdog kicker functions */ +static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer) +{ + unsigned long touch_ts = __this_cpu_read(watchdog_touch_ts); + struct pt_regs *regs = get_irq_regs(); + int duration; + int softlockup_all_cpu_backtrace = sysctl_softlockup_all_cpu_backtrace; + + /* kick the hardlockup detector */ + watchdog_interrupt_count(); + + /* kick the softlockup detector */ + wake_up_process(__this_cpu_read(softlockup_watchdog)); + + /* .. and repeat */ + hrtimer_forward_now(hrtimer, ns_to_ktime(sample_period)); + + if (touch_ts == 0) { + if (unlikely(__this_cpu_read(softlockup_touch_sync))) { + /* + * If the time stamp was touched atomically + * make sure the scheduler tick is up to date. + */ + __this_cpu_write(softlockup_touch_sync, false); + sched_clock_tick(); + } + + /* Clear the guest paused flag on watchdog reset */ + kvm_check_and_clear_guest_paused(); + __touch_watchdog(); + return HRTIMER_RESTART; + } + + /* check for a softlockup + * This is done by making sure a high priority task is + * being scheduled. The task touches the watchdog to + * indicate it is getting cpu time. If it hasn't then + * this is a good indication some task is hogging the cpu + */ + duration = is_softlockup(touch_ts); + if (unlikely(duration)) { + /* + * If a virtual machine is stopped by the host it can look to + * the watchdog like a soft lockup, check to see if the host + * stopped the vm before we issue the warning + */ + if (kvm_check_and_clear_guest_paused()) + return HRTIMER_RESTART; + + /* only warn once */ + if (__this_cpu_read(soft_watchdog_warn) == true) { + /* + * When multiple processes are causing softlockups the + * softlockup detector only warns on the first one + * because the code relies on a full quiet cycle to + * re-arm. The second process prevents the quiet cycle + * and never gets reported. Use task pointers to detect + * this. + */ + if (__this_cpu_read(softlockup_task_ptr_saved) != + current) { + __this_cpu_write(soft_watchdog_warn, false); + __touch_watchdog(); + } + return HRTIMER_RESTART; + } + + if (softlockup_all_cpu_backtrace) { + /* Prevent multiple soft-lockup reports if one cpu is already + * engaged in dumping cpu back traces + */ + if (test_and_set_bit(0, &soft_lockup_nmi_warn)) { + /* Someone else will report us. Let's give up */ + __this_cpu_write(soft_watchdog_warn, true); + return HRTIMER_RESTART; + } + } + + pr_emerg("BUG: soft lockup - CPU#%d stuck for %us! [%s:%d]\n", + smp_processor_id(), duration, + current->comm, task_pid_nr(current)); + __this_cpu_write(softlockup_task_ptr_saved, current); + print_modules(); + print_irqtrace_events(current); + if (regs) + show_regs(regs); + else + dump_stack(); + + if (softlockup_all_cpu_backtrace) { + /* Avoid generating two back traces for current + * given that one is already made above + */ + trigger_allbutself_cpu_backtrace(); + + clear_bit(0, &soft_lockup_nmi_warn); + /* Barrier to sync with other cpus */ + smp_mb__after_atomic(); + } + + add_taint(TAINT_SOFTLOCKUP, LOCKDEP_STILL_OK); + if (softlockup_panic) + panic("softlockup: hung tasks"); + __this_cpu_write(soft_watchdog_warn, true); + } else + __this_cpu_write(soft_watchdog_warn, false); + + return HRTIMER_RESTART; +} + +static void watchdog_set_prio(unsigned int policy, unsigned int prio) +{ + struct sched_param param = { .sched_priority = prio }; + + sched_setscheduler(current, policy, ¶m); +} + +static void watchdog_enable(unsigned int cpu) +{ + struct hrtimer *hrtimer = raw_cpu_ptr(&watchdog_hrtimer); + + /* kick off the timer for the hardlockup detector */ + hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL); + hrtimer->function = watchdog_timer_fn; + + /* Enable the perf event */ + watchdog_nmi_enable(cpu); + + /* done here because hrtimer_start can only pin to smp_processor_id() */ + hrtimer_start(hrtimer, ns_to_ktime(sample_period), + HRTIMER_MODE_REL_PINNED); + + /* initialize timestamp */ + watchdog_set_prio(SCHED_FIFO, MAX_RT_PRIO - 1); + __touch_watchdog(); +} + +static void watchdog_disable(unsigned int cpu) +{ + struct hrtimer *hrtimer = raw_cpu_ptr(&watchdog_hrtimer); + + watchdog_set_prio(SCHED_NORMAL, 0); + hrtimer_cancel(hrtimer); + /* disable the perf event */ + watchdog_nmi_disable(cpu); +} + +static void watchdog_cleanup(unsigned int cpu, bool online) +{ + watchdog_disable(cpu); +} + +static int watchdog_should_run(unsigned int cpu) +{ + return __this_cpu_read(hrtimer_interrupts) != + __this_cpu_read(soft_lockup_hrtimer_cnt); +} + +/* + * The watchdog thread function - touches the timestamp. + * + * It only runs once every sample_period seconds (4 seconds by + * default) to reset the softlockup timestamp. If this gets delayed + * for more than 2*watchdog_thresh seconds then the debug-printout + * triggers in watchdog_timer_fn(). + */ +static void watchdog(unsigned int cpu) +{ + __this_cpu_write(soft_lockup_hrtimer_cnt, + __this_cpu_read(hrtimer_interrupts)); + __touch_watchdog(); + + /* + * watchdog_nmi_enable() clears the NMI_WATCHDOG_ENABLED bit in the + * failure path. Check for failures that can occur asynchronously - + * for example, when CPUs are on-lined - and shut down the hardware + * perf event on each CPU accordingly. + * + * The only non-obvious place this bit can be cleared is through + * watchdog_nmi_enable(), so a pr_info() is placed there. Placing a + * pr_info here would be too noisy as it would result in a message + * every few seconds if the hardlockup was disabled but the softlockup + * enabled. + */ + if (!(watchdog_enabled & NMI_WATCHDOG_ENABLED)) + watchdog_nmi_disable(cpu); +} + +#ifdef CONFIG_HARDLOCKUP_DETECTOR +/* + * People like the simple clean cpu node info on boot. + * Reduce the watchdog noise by only printing messages + * that are different from what cpu0 displayed. + */ +static unsigned long cpu0_err; + +static int watchdog_nmi_enable(unsigned int cpu) +{ + struct perf_event_attr *wd_attr; + struct perf_event *event = per_cpu(watchdog_ev, cpu); + + /* nothing to do if the hard lockup detector is disabled */ + if (!(watchdog_enabled & NMI_WATCHDOG_ENABLED)) + goto out; + + /* is it already setup and enabled? */ + if (event && event->state > PERF_EVENT_STATE_OFF) + goto out; + + /* it is setup but not enabled */ + if (event != NULL) + goto out_enable; + + wd_attr = &wd_hw_attr; + wd_attr->sample_period = hw_nmi_get_sample_period(watchdog_thresh); + + /* Try to register using hardware perf events */ + event = perf_event_create_kernel_counter(wd_attr, cpu, NULL, watchdog_overflow_callback, NULL); + + /* save cpu0 error for future comparision */ + if (cpu == 0 && IS_ERR(event)) + cpu0_err = PTR_ERR(event); + + if (!IS_ERR(event)) { + /* only print for cpu0 or different than cpu0 */ + if (cpu == 0 || cpu0_err) + pr_info("enabled on all CPUs, permanently consumes one hw-PMU counter.\n"); + goto out_save; + } + + /* + * Disable the hard lockup detector if _any_ CPU fails to set up + * set up the hardware perf event. The watchdog() function checks + * the NMI_WATCHDOG_ENABLED bit periodically. + * + * The barriers are for syncing up watchdog_enabled across all the + * cpus, as clear_bit() does not use barriers. + */ + smp_mb__before_atomic(); + clear_bit(NMI_WATCHDOG_ENABLED_BIT, &watchdog_enabled); + smp_mb__after_atomic(); + + /* skip displaying the same error again */ + if (cpu > 0 && (PTR_ERR(event) == cpu0_err)) + return PTR_ERR(event); + + /* vary the KERN level based on the returned errno */ + if (PTR_ERR(event) == -EOPNOTSUPP) + pr_info("disabled (cpu%i): not supported (no LAPIC?)\n", cpu); + else if (PTR_ERR(event) == -ENOENT) + pr_warn("disabled (cpu%i): hardware events not enabled\n", + cpu); + else + pr_err("disabled (cpu%i): unable to create perf event: %ld\n", + cpu, PTR_ERR(event)); + + pr_info("Shutting down hard lockup detector on all cpus\n"); + + return PTR_ERR(event); + + /* success path */ +out_save: + per_cpu(watchdog_ev, cpu) = event; +out_enable: + perf_event_enable(per_cpu(watchdog_ev, cpu)); +out: + return 0; +} + +static void watchdog_nmi_disable(unsigned int cpu) +{ + struct perf_event *event = per_cpu(watchdog_ev, cpu); + + if (event) { + perf_event_disable(event); + per_cpu(watchdog_ev, cpu) = NULL; + + /* should be in cleanup, but blocks oprofile */ + perf_event_release_kernel(event); + } + if (cpu == 0) { + /* watchdog_nmi_enable() expects this to be zero initially. */ + cpu0_err = 0; + } +} + +void watchdog_nmi_enable_all(void) +{ + int cpu; + + mutex_lock(&watchdog_proc_mutex); + + if (!(watchdog_enabled & NMI_WATCHDOG_ENABLED)) + goto unlock; + + get_online_cpus(); + for_each_online_cpu(cpu) + watchdog_nmi_enable(cpu); + put_online_cpus(); + +unlock: + mutex_unlock(&watchdog_proc_mutex); +} + +void watchdog_nmi_disable_all(void) +{ + int cpu; + + mutex_lock(&watchdog_proc_mutex); + + if (!watchdog_running) + goto unlock; + + get_online_cpus(); + for_each_online_cpu(cpu) + watchdog_nmi_disable(cpu); + put_online_cpus(); + +unlock: + mutex_unlock(&watchdog_proc_mutex); +} +#else +static int watchdog_nmi_enable(unsigned int cpu) { return 0; } +static void watchdog_nmi_disable(unsigned int cpu) { return; } +void watchdog_nmi_enable_all(void) {} +void watchdog_nmi_disable_all(void) {} +#endif /* CONFIG_HARDLOCKUP_DETECTOR */ + +static struct smp_hotplug_thread watchdog_threads = { + .store = &softlockup_watchdog, + .thread_should_run = watchdog_should_run, + .thread_fn = watchdog, + .thread_comm = "watchdog/%u", + .setup = watchdog_enable, + .cleanup = watchdog_cleanup, + .park = watchdog_disable, + .unpark = watchdog_enable, +}; + +static void restart_watchdog_hrtimer(void *info) +{ + struct hrtimer *hrtimer = raw_cpu_ptr(&watchdog_hrtimer); + int ret; + + /* + * No need to cancel and restart hrtimer if it is currently executing + * because it will reprogram itself with the new period now. + * We should never see it unqueued here because we are running per-cpu + * with interrupts disabled. + */ + ret = hrtimer_try_to_cancel(hrtimer); + if (ret == 1) + hrtimer_start(hrtimer, ns_to_ktime(sample_period), + HRTIMER_MODE_REL_PINNED); +} + +static void update_watchdog(int cpu) +{ + /* + * Make sure that perf event counter will adopt to a new + * sampling period. Updating the sampling period directly would + * be much nicer but we do not have an API for that now so + * let's use a big hammer. + * Hrtimer will adopt the new period on the next tick but this + * might be late already so we have to restart the timer as well. + */ + watchdog_nmi_disable(cpu); + smp_call_function_single(cpu, restart_watchdog_hrtimer, NULL, 1); + watchdog_nmi_enable(cpu); +} + +static void update_watchdog_all_cpus(void) +{ + int cpu; + + get_online_cpus(); + for_each_online_cpu(cpu) + update_watchdog(cpu); + put_online_cpus(); +} + +static int watchdog_enable_all_cpus(void) +{ + int err = 0; + + if (!watchdog_running) { + err = smpboot_register_percpu_thread(&watchdog_threads); + if (err) + pr_err("Failed to create watchdog threads, disabled\n"); + else + watchdog_running = 1; + } else { + /* + * Enable/disable the lockup detectors or + * change the sample period 'on the fly'. + */ + update_watchdog_all_cpus(); + } + + return err; +} + +/* prepare/enable/disable routines */ +/* sysctl functions */ +#ifdef CONFIG_SYSCTL +static void watchdog_disable_all_cpus(void) +{ + if (watchdog_running) { + watchdog_running = 0; + smpboot_unregister_percpu_thread(&watchdog_threads); + } +} + +/* + * Update the run state of the lockup detectors. + */ +static int proc_watchdog_update(void) +{ + int err = 0; + + /* + * Watchdog threads won't be started if they are already active. + * The 'watchdog_running' variable in watchdog_*_all_cpus() takes + * care of this. If those threads are already active, the sample + * period will be updated and the lockup detectors will be enabled + * or disabled 'on the fly'. + */ + if (watchdog_enabled && watchdog_thresh) + err = watchdog_enable_all_cpus(); + else + watchdog_disable_all_cpus(); + + return err; + +} + +/* + * common function for watchdog, nmi_watchdog and soft_watchdog parameter + * + * caller | table->data points to | 'which' contains the flag(s) + * -------------------|-----------------------|----------------------------- + * proc_watchdog | watchdog_user_enabled | NMI_WATCHDOG_ENABLED or'ed + * | | with SOFT_WATCHDOG_ENABLED + * -------------------|-----------------------|----------------------------- + * proc_nmi_watchdog | nmi_watchdog_enabled | NMI_WATCHDOG_ENABLED + * -------------------|-----------------------|----------------------------- + * proc_soft_watchdog | soft_watchdog_enabled | SOFT_WATCHDOG_ENABLED + */ +static int proc_watchdog_common(int which, struct ctl_table *table, int write, + void __user *buffer, size_t *lenp, loff_t *ppos) +{ + int err, old, new; + int *watchdog_param = (int *)table->data; + + mutex_lock(&watchdog_proc_mutex); + + /* + * If the parameter is being read return the state of the corresponding + * bit(s) in 'watchdog_enabled', else update 'watchdog_enabled' and the + * run state of the lockup detectors. + */ + if (!write) { + *watchdog_param = (watchdog_enabled & which) != 0; + err = proc_dointvec_minmax(table, write, buffer, lenp, ppos); + } else { + err = proc_dointvec_minmax(table, write, buffer, lenp, ppos); + if (err) + goto out; + + /* + * There is a race window between fetching the current value + * from 'watchdog_enabled' and storing the new value. During + * this race window, watchdog_nmi_enable() can sneak in and + * clear the NMI_WATCHDOG_ENABLED bit in 'watchdog_enabled'. + * The 'cmpxchg' detects this race and the loop retries. + */ + do { + old = watchdog_enabled; + /* + * If the parameter value is not zero set the + * corresponding bit(s), else clear it(them). + */ + if (*watchdog_param) + new = old | which; + else + new = old & ~which; + } while (cmpxchg(&watchdog_enabled, old, new) != old); + + /* + * Update the run state of the lockup detectors. + * Restore 'watchdog_enabled' on failure. + */ + err = proc_watchdog_update(); + if (err) + watchdog_enabled = old; + } +out: + mutex_unlock(&watchdog_proc_mutex); + return err; +} + +/* + * /proc/sys/kernel/watchdog + */ +int proc_watchdog(struct ctl_table *table, int write, + void __user *buffer, size_t *lenp, loff_t *ppos) +{ + return proc_watchdog_common(NMI_WATCHDOG_ENABLED|SOFT_WATCHDOG_ENABLED, + table, write, buffer, lenp, ppos); +} + +/* + * /proc/sys/kernel/nmi_watchdog + */ +int proc_nmi_watchdog(struct ctl_table *table, int write, + void __user *buffer, size_t *lenp, loff_t *ppos) +{ + return proc_watchdog_common(NMI_WATCHDOG_ENABLED, + table, write, buffer, lenp, ppos); +} + +/* + * /proc/sys/kernel/soft_watchdog + */ +int proc_soft_watchdog(struct ctl_table *table, int write, + void __user *buffer, size_t *lenp, loff_t *ppos) +{ + return proc_watchdog_common(SOFT_WATCHDOG_ENABLED, + table, write, buffer, lenp, ppos); +} + +/* + * /proc/sys/kernel/watchdog_thresh + */ +int proc_watchdog_thresh(struct ctl_table *table, int write, + void __user *buffer, size_t *lenp, loff_t *ppos) +{ + int err, old; + + mutex_lock(&watchdog_proc_mutex); + + old = ACCESS_ONCE(watchdog_thresh); + err = proc_dointvec_minmax(table, write, buffer, lenp, ppos); + + if (err || !write) + goto out; + + /* + * Update the sample period. + * Restore 'watchdog_thresh' on failure. + */ + set_sample_period(); + err = proc_watchdog_update(); + if (err) + watchdog_thresh = old; +out: + mutex_unlock(&watchdog_proc_mutex); + return err; +} +#endif /* CONFIG_SYSCTL */ + +void __init lockup_detector_init(void) +{ + set_sample_period(); + + if (watchdog_enabled) + watchdog_enable_all_cpus(); +} |