1 files changed, 113 insertions, 0 deletions
diff --git a/kernel/watchdog_buddy.c b/kernel/watchdog_buddy.c
new file mode 100644
index 0000000000..34dbfe091f
--- /dev/null
+++ b/kernel/watchdog_buddy.c
@@ -0,0 +1,113 @@
+// 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 cpumask_t __read_mostly watchdog_cpus;
+
+static unsigned int watchdog_next_cpu(unsigned int cpu)
+{
+	unsigned int next_cpu;
+
+	next_cpu = cpumask_next(cpu, &watchdog_cpus);
+	if (next_cpu >= nr_cpu_ids)
+		next_cpu = cpumask_first(&watchdog_cpus);
+
+	if (next_cpu == cpu)
+		return nr_cpu_ids;
+
+	return next_cpu;
+}
+
+int __init watchdog_hardlockup_probe(void)
+{
+	return 0;
+}
+
+void watchdog_hardlockup_enable(unsigned int cpu)
+{
+	unsigned int next_cpu;
+
+	/*
+	 * The new CPU will be marked online before the hrtimer interrupt
+	 * gets a chance to run on it. If another CPU tests for a
+	 * hardlockup on the new CPU before it has run its the hrtimer
+	 * interrupt, it will get a false positive. Touch the watchdog on
+	 * the new CPU to delay the check for at least 3 sampling periods
+	 * to guarantee one hrtimer has run on the new CPU.
+	 */
+	watchdog_hardlockup_touch_cpu(cpu);
+
+	/*
+	 * We are going to check the next CPU. Our watchdog_hrtimer
+	 * need not be zero if the CPU has already been online earlier.
+	 * Touch the watchdog on the next CPU to avoid false positive
+	 * if we try to check it in less then 3 interrupts.
+	 */
+	next_cpu = watchdog_next_cpu(cpu);
+	if (next_cpu < nr_cpu_ids)
+		watchdog_hardlockup_touch_cpu(next_cpu);
+
+	/*
+	 * Makes sure that watchdog is touched on this CPU before
+	 * other CPUs could see it in watchdog_cpus. The counter
+	 * part is in watchdog_buddy_check_hardlockup().
+	 */
+	smp_wmb();
+
+	cpumask_set_cpu(cpu, &watchdog_cpus);
+}
+
+void watchdog_hardlockup_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)
+		watchdog_hardlockup_touch_cpu(next_cpu);
+
+	/*
+	 * Makes sure that watchdog is touched on the next CPU before
+	 * this CPU disappear in watchdog_cpus. The counter part is in
+	 * watchdog_buddy_check_hardlockup().
+	 */
+	smp_wmb();
+
+	cpumask_clear_cpu(cpu, &watchdog_cpus);
+}
+
+void watchdog_buddy_check_hardlockup(int hrtimer_interrupts)
+{
+	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 (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;
+
+	/*
+	 * Make sure that the watchdog was touched on next CPU when
+	 * watchdog_next_cpu() returned another one because of
+	 * a change in watchdog_hardlockup_enable()/disable().
+	 */
+	smp_rmb();
+
+	watchdog_hardlockup_check(next_cpu, NULL);
+}