[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>

12 files changed, 201 insertions, 0 deletions

diff --git a/arch/i386/kernel/nmi.c b/arch/i386/kernel/nmi.c
index 8bbdbda07a2d..0178457db721 100644
--- a/arch/i386/kernel/nmi.c
+++ b/arch/i386/kernel/nmi.c
@@ -478,6 +478,11 @@ void touch_nmi_watchdog (void)
          */
         for (i = 0; i < NR_CPUS; i++)
                 alert_counter[i] = 0;
+
+        /*
+         * Tickle the softlockup detector too:
+         */
+        touch_softlockup_watchdog();
 }
 
 extern void die_nmi(struct pt_regs *, const char *msg);
diff --git a/arch/i386/kernel/time.c b/arch/i386/kernel/time.c
index 6f794a78ee1e..b0c5ee2b3446 100644
--- a/arch/i386/kernel/time.c
+++ b/arch/i386/kernel/time.c
@@ -422,6 +422,7 @@ static int timer_resume(struct sys_device *dev)
                 last_timer->resume();
         cur_timer = last_timer;
         last_timer = NULL;
+        touch_softlockup_watchdog();
         return 0;
 }
 
diff --git a/arch/x86_64/kernel/nmi.c b/arch/x86_64/kernel/nmi.c
index 64a8e05d5811..84cae81fff8b 100644
--- a/arch/x86_64/kernel/nmi.c
+++ b/arch/x86_64/kernel/nmi.c
@@ -463,6 +463,8 @@ void touch_nmi_watchdog (void)
          */
         for (i = 0; i < NR_CPUS; i++)
                 per_cpu(nmi_touch, i) = 1;
+
+        touch_softlockup_watchdog();
 }
 
 void nmi_watchdog_tick (struct pt_regs * regs, unsigned reason)
diff --git a/arch/x86_64/kernel/time.c b/arch/x86_64/kernel/time.c
index 66bf6ddeb0c3..2b5d9da912a2 100644
--- a/arch/x86_64/kernel/time.c
+++ b/arch/x86_64/kernel/time.c
@@ -1041,6 +1041,7 @@ static int timer_resume(struct sys_device *dev)
         write_sequnlock_irqrestore(&xtime_lock,flags);
         jiffies += sleep_length;
         wall_jiffies += sleep_length;
+        touch_softlockup_watchdog();
         return 0;
 }
 
diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
index eee5115658c8..04e54318bc6a 100644
--- a/drivers/mtd/nand/nand_base.c
+++ b/drivers/mtd/nand/nand_base.c
@@ -526,6 +526,7 @@ static void nand_wait_ready(struct mtd_info *mtd)
         do {
                 if (this->dev_ready(mtd))
                         return;
+                touch_softlockup_watchdog();
         } while (time_before(jiffies, timeo));  
 }
 
diff --git a/include/linux/sched.h b/include/linux/sched.h
index dec5827c7742..5fb31bede103 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -176,6 +176,23 @@ extern void trap_init(void);
 extern void update_process_times(int user);
 extern void scheduler_tick(void);
 
+#ifdef CONFIG_DETECT_SOFTLOCKUP
+extern void softlockup_tick(struct pt_regs *regs);
+extern void spawn_softlockup_task(void);
+extern void touch_softlockup_watchdog(void);
+#else
+static inline void softlockup_tick(struct pt_regs *regs)
+{
+}
+static inline void spawn_softlockup_task(void)
+{
+}
+static inline void touch_softlockup_watchdog(void)
+{
+}
+#endif
+
+
 /* Attach to any functions which should be ignored in wchan output. */
 #define __sched         __attribute__((__section__(".sched.text")))
 /* Is this address in the __sched functions? */
diff --git a/init/main.c b/init/main.c
index ff410063e4e1..a29fb2ac7240 100644
--- a/init/main.c
+++ b/init/main.c
@@ -614,6 +614,7 @@ static void do_pre_smp_initcalls(void)
         migration_init();
 #endif
         spawn_ksoftirqd();
+        spawn_softlockup_task();
 }
 
 static void run_init_process(char *init_filename)
diff --git a/kernel/Makefile b/kernel/Makefile
index cb05cd05d237..8d57a2f1226b 100644
--- a/kernel/Makefile
+++ b/kernel/Makefile
@@ -27,6 +27,7 @@ obj-$(CONFIG_AUDIT) += audit.o
 obj-$(CONFIG_AUDITSYSCALL) += auditsc.o
 obj-$(CONFIG_KPROBES) += kprobes.o
 obj-$(CONFIG_SYSFS) += ksysfs.o
+obj-$(CONFIG_DETECT_SOFTLOCKUP) += softlockup.o
 obj-$(CONFIG_GENERIC_HARDIRQS) += irq/
 obj-$(CONFIG_CRASH_DUMP) += crash_dump.o
 obj-$(CONFIG_SECCOMP) += seccomp.o
diff --git a/kernel/power/swsusp.c b/kernel/power/swsusp.c
index eaacd5cb5889..d967e875ee82 100644
--- a/kernel/power/swsusp.c
+++ b/kernel/power/swsusp.c
@@ -1059,6 +1059,7 @@ int swsusp_resume(void)
         BUG_ON(!error);
         restore_processor_state();
         restore_highmem();
+        touch_softlockup_watchdog();
         device_power_up();
         local_irq_enable();
         return error;
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);
+}
+
diff --git a/kernel/timer.c b/kernel/timer.c
index 5377f40723ff..1433d87f46b3 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -950,6 +950,7 @@ void do_timer(struct pt_regs *regs)
 {
         jiffies_64++;
         update_times();
+        softlockup_tick(regs);
 }
 
 #ifdef __ARCH_WANT_SYS_ALARM
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 299f7f3b5b08..3754c9a8f5c8 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -46,6 +46,25 @@ config LOG_BUF_SHIFT
                      13 =>  8 KB
                      12 =>  4 KB
 
+config DETECT_SOFTLOCKUP
+        bool "Detect Soft Lockups"
+        depends on DEBUG_KERNEL
+        default y
+        help
+          Say Y here to enable the kernel to detect "soft lockups",
+          which are bugs that cause the kernel to loop in kernel
+          mode for more than 10 seconds, without giving other tasks a
+          chance to run.
+
+          When a soft-lockup is detected, the kernel will print the
+          current stack trace (which you should report), but the
+          system will stay locked up. This feature has negligible
+          overhead.
+
+          (Note that "hard lockups" are separate type of bugs that
+           can be detected via the NMI-watchdog, on platforms that
+           support it.)
+
 config SCHEDSTATS
         bool "Collect scheduler statistics"
         depends on DEBUG_KERNEL && PROC_FS