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// SPDX-License-Identifier: GPL-2.0
#include <linux/cpu.h>
#include <linux/cpumask.h>
#include <linux/kernel.h>
#include <linux/nmi.h>
#include <linux/percpu-defs.h>
static DEFINE_PER_CPU(bool, watchdog_touch);
static DEFINE_PER_CPU(bool, hard_watchdog_warn);
static cpumask_t __read_mostly watchdog_cpus;
int __init watchdog_nmi_probe(void)
{
return 0;
}
notrace void buddy_cpu_touch_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_touch, true);
}
EXPORT_SYMBOL_GPL(buddy_cpu_touch_watchdog);
static unsigned int watchdog_next_cpu(unsigned int cpu)
{
cpumask_t cpus = watchdog_cpus;
unsigned int next_cpu;
next_cpu = cpumask_next(cpu, &cpus);
if (next_cpu >= nr_cpu_ids)
next_cpu = cpumask_first(&cpus);
if (next_cpu == cpu)
return nr_cpu_ids;
return next_cpu;
}
int watchdog_nmi_enable(unsigned int cpu)
{
/*
* The new cpu will be marked online before the first hrtimer interrupt
* runs on it. If another cpu tests for a hardlockup on the new cpu
* before it has run its first hrtimer, it will get a false positive.
* Touch the watchdog on the new cpu to delay the first check for at
* least 3 sampling periods to guarantee one hrtimer has run on the new
* cpu.
*/
per_cpu(watchdog_touch, cpu) = true;
smp_wmb();
cpumask_set_cpu(cpu, &watchdog_cpus);
return 0;
}
void watchdog_nmi_disable(unsigned int cpu)
{
unsigned int next_cpu = watchdog_next_cpu(cpu);
/*
* Offlining this cpu will cause the cpu before this one to start
* checking the one after this one. If this cpu just finished checking
* the next cpu and updating hrtimer_interrupts_saved, and then the
* previous cpu checks it within one sample period, it will trigger a
* false positive. Touch the watchdog on the next cpu to prevent it.
*/
if (next_cpu < nr_cpu_ids)
per_cpu(watchdog_touch, next_cpu) = true;
smp_wmb();
cpumask_clear_cpu(cpu, &watchdog_cpus);
}
static int is_hardlockup_buddy_cpu(unsigned int cpu)
{
unsigned long hrint = per_cpu(hrtimer_interrupts, cpu);
if (per_cpu(hrtimer_interrupts_saved, cpu) == hrint)
return 1;
per_cpu(hrtimer_interrupts_saved, cpu) = hrint;
return 0;
}
void watchdog_check_hardlockup(void)
{
unsigned int next_cpu;
/*
* Test for hardlockups every 3 samples. The sample period is
* watchdog_thresh * 2 / 5, so 3 samples gets us back to slightly over
* watchdog_thresh (over by 20%).
*/
if (__this_cpu_read(hrtimer_interrupts) % 3 != 0)
return;
/* check for a hardlockup on the next cpu */
next_cpu = watchdog_next_cpu(smp_processor_id());
if (next_cpu >= nr_cpu_ids)
return;
smp_rmb();
if (per_cpu(watchdog_touch, next_cpu) == true) {
per_cpu(watchdog_touch, next_cpu) = false;
return;
}
if (is_hardlockup_buddy_cpu(next_cpu)) {
/* only warn once */
if (per_cpu(hard_watchdog_warn, next_cpu) == true)
return;
if (hardlockup_panic)
panic("Watchdog detected hard LOCKUP on cpu %u", next_cpu);
else
WARN(1, "Watchdog detected hard LOCKUP on cpu %u", next_cpu);
per_cpu(hard_watchdog_warn, next_cpu) = true;
} else {
per_cpu(hard_watchdog_warn, next_cpu) = false;
}
}
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