[PATCH] detect soft lockups

This patch adds a new kernel debug feature: CONFIG_DETECT_SOFTLOCKUP.

When enabled then per-CPU watchdog threads are started, which try to run
once per second.  If they get delayed for more than 10 seconds then a
callback from the timer interrupt detects this condition and prints out a
warning message and a stack dump (once per lockup incident).  The feature
is otherwise non-intrusive, it doesnt try to unlock the box in any way, it
only gets the debug info out, automatically, and on all CPUs affected by
the lockup.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Nishanth Aravamudan <nacc@us.ibm.com>
Signed-Off-By: Matthias Urlichs <smurf@smurf.noris.de>
Signed-off-by: Richard Purdie <rpurdie@rpsys.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 151 insertions, 0 deletions

diff --git a/kernel/softlockup.c b/kernel/softlockup.c
new file mode 100644
index 000000000000..75976209cea7
--- /dev/null
+++ b/kernel/softlockup.c
@@ -0,0 +1,151 @@
+/*
+ * Detect Soft Lockups
+ *
+ * started by Ingo Molnar, (C) 2005, Red Hat
+ *
+ * this code detects soft lockups: incidents in where on a CPU
+ * the kernel does not reschedule for 10 seconds or more.
+ */
+
+#include <linux/mm.h>
+#include <linux/cpu.h>
+#include <linux/init.h>
+#include <linux/delay.h>
+#include <linux/kthread.h>
+#include <linux/notifier.h>
+#include <linux/module.h>
+
+static DEFINE_SPINLOCK(print_lock);
+
+static DEFINE_PER_CPU(unsigned long, timestamp) = 0;
+static DEFINE_PER_CPU(unsigned long, print_timestamp) = 0;
+static DEFINE_PER_CPU(struct task_struct *, watchdog_task);
+
+static int did_panic = 0;
+static int softlock_panic(struct notifier_block *this, unsigned long event,
+                                void *ptr)
+{
+        did_panic = 1;
+
+        return NOTIFY_DONE;
+}
+
+static struct notifier_block panic_block = {
+        .notifier_call = softlock_panic,
+};
+
+void touch_softlockup_watchdog(void)
+{
+        per_cpu(timestamp, raw_smp_processor_id()) = jiffies;
+}
+EXPORT_SYMBOL(touch_softlockup_watchdog);
+
+/*
+ * This callback runs from the timer interrupt, and checks
+ * whether the watchdog thread has hung or not:
+ */
+void softlockup_tick(struct pt_regs *regs)
+{
+        int this_cpu = smp_processor_id();
+        unsigned long timestamp = per_cpu(timestamp, this_cpu);
+
+        if (per_cpu(print_timestamp, this_cpu) == timestamp)
+                return;
+
+        /* Do not cause a second panic when there already was one */
+        if (did_panic)
+                return;
+
+        if (time_after(jiffies, timestamp + 10*HZ)) {
+                per_cpu(print_timestamp, this_cpu) = timestamp;
+
+                spin_lock(&print_lock);
+                printk(KERN_ERR "BUG: soft lockup detected on CPU#%d!\n",
+                        this_cpu);
+                show_regs(regs);
+                spin_unlock(&print_lock);
+        }
+}
+
+/*
+ * The watchdog thread - runs every second and touches the timestamp.
+ */
+static int watchdog(void * __bind_cpu)
+{
+        struct sched_param param = { .sched_priority = 99 };
+        int this_cpu = (long) __bind_cpu;
+
+        printk("softlockup thread %d started up.\n", this_cpu);
+
+        sched_setscheduler(current, SCHED_FIFO, &param);
+        current->flags |= PF_NOFREEZE;
+
+        set_current_state(TASK_INTERRUPTIBLE);
+
+        /*
+         * Run briefly once per second - if this gets delayed for
+         * more than 10 seconds then the debug-printout triggers
+         * in softlockup_tick():
+         */
+        while (!kthread_should_stop()) {
+                msleep_interruptible(1000);
+                touch_softlockup_watchdog();
+        }
+        __set_current_state(TASK_RUNNING);
+
+        return 0;
+}
+
+/*
+ * Create/destroy watchdog threads as CPUs come and go:
+ */
+static int __devinit
+cpu_callback(struct notifier_block *nfb, unsigned long action, void *hcpu)
+{
+        int hotcpu = (unsigned long)hcpu;
+        struct task_struct *p;
+
+        switch (action) {
+        case CPU_UP_PREPARE:
+                BUG_ON(per_cpu(watchdog_task, hotcpu));
+                p = kthread_create(watchdog, hcpu, "watchdog/%d", hotcpu);
+                if (IS_ERR(p)) {
+                        printk("watchdog for %i failed\n", hotcpu);
+                        return NOTIFY_BAD;
+                }
+                per_cpu(watchdog_task, hotcpu) = p;
+                kthread_bind(p, hotcpu);
+                break;
+        case CPU_ONLINE:
+
+                wake_up_process(per_cpu(watchdog_task, hotcpu));
+                break;
+#ifdef CONFIG_HOTPLUG_CPU
+        case CPU_UP_CANCELED:
+                /* Unbind so it can run.  Fall thru. */
+                kthread_bind(per_cpu(watchdog_task, hotcpu), smp_processor_id());
+        case CPU_DEAD:
+                p = per_cpu(watchdog_task, hotcpu);
+                per_cpu(watchdog_task, hotcpu) = NULL;
+                kthread_stop(p);
+                break;
+#endif /* CONFIG_HOTPLUG_CPU */
+        }
+        return NOTIFY_OK;
+}
+
+static struct notifier_block __devinitdata cpu_nfb = {
+        .notifier_call = cpu_callback
+};
+
+__init void spawn_softlockup_task(void)
+{
+        void *cpu = (void *)(long)smp_processor_id();
+
+        cpu_callback(&cpu_nfb, CPU_UP_PREPARE, cpu);
+        cpu_callback(&cpu_nfb, CPU_ONLINE, cpu);
+        register_cpu_notifier(&cpu_nfb);
+
+        notifier_chain_register(&panic_notifier_list, &panic_block);
+}
+