Re: [patch] Real-Time Preemption, -RT-2.6.13-rc4-V0.7.52-01

Steven Rostedt
2005-08-03T16:44:42Z

Ingo,

Doing some more tests on the patch, I found that I don't like the
placement in sched.c of the touch_light_softlockup_watchdog. I figure
that it may be better to put in into __schedule instead. This really
shows where a task is taken off the run queue.

-- Steve

New patch: I've only tested this with the deadlock modules, and not with
the kjournald case. I'll do that tonight when I'm no longer needing my
computer for other tests.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

Index: linux_realtime_ernie/kernel/irq/handle.c
===================================================================
--- linux_realtime_ernie/kernel/irq/handle.c (revision 266)
+++ linux_realtime_ernie/kernel/irq/handle.c (working copy)
@@ -177,6 +177,14 @@
*/
local_irq_save(flags);
#endif
+ /*
+ * If the task is currently running in user mode, don't
+ * detect soft lockups. If CONFIG_DETECT_SOFTLOCKUP is not
+ * configured, this should be optimized out.
+ */
+ if (user_mode(regs))
+ touch_light_softlockup_watchdog();
+
kstat_this_cpu.irqs[irq]++;
if (desc->status & IRQ_PER_CPU) {
irqreturn_t action_ret;
Index: linux_realtime_ernie/kernel/sched.c
===================================================================
--- linux_realtime_ernie/kernel/sched.c (revision 266)
+++ linux_realtime_ernie/kernel/sched.c (working copy)
@@ -3209,6 +3209,7 @@
else {
if (prev->state == TASK_UNINTERRUPTIBLE)
rq->nr_uninterruptible++;
+ touch_light_softlockup_watchdog();
deactivate_task(prev, rq);
}
}
Index: linux_realtime_ernie/kernel/softlockup.c
===================================================================
--- linux_realtime_ernie/kernel/softlockup.c (revision 269)
+++ linux_realtime_ernie/kernel/softlockup.c (working copy)
@@ -3,6 +3,10 @@
*
* started by Ingo Molnar, (C) 2005, Red Hat
*
+ * Steven Rostedt, Kihon Technologies Inc.
+ * Added light softlockup detection off of what Daniel Walker of
+ * MontaVista started.
+ *
* this code detects soft lockups: incidents in where on a CPU
* the kernel does not reschedule for 10 seconds or more.
*/
@@ -20,9 +24,7 @@
static DEFINE_PER_CPU(unsigned long, timeout) = INITIAL_JIFFIES;
static DEFINE_PER_CPU(unsigned long, timestamp) = INITIAL_JIFFIES;
static DEFINE_PER_CPU(unsigned long, print_timestamp) = INITIAL_JIFFIES;
-static DEFINE_PER_CPU(struct task_struct *, prev_task);
static DEFINE_PER_CPU(struct task_struct *, watchdog_task);
-static DEFINE_PER_CPU(unsigned long, task_counter);

static int did_panic = 0;
static int softlock_panic(struct notifier_block *this, unsigned long event,
@@ -42,6 +44,11 @@
per_cpu(timestamp, raw_smp_processor_id()) = jiffies;
}

+void touch_light_softlockup_watchdog(void)
+{
+ current->softlockup_count = 0;
+}
+
/*
* This callback runs from the timer interrupt, and checks
* whether the watchdog thread has hung or not:
@@ -59,24 +66,20 @@
if (!per_cpu(watchdog_task, this_cpu))
return;

- if (per_cpu(prev_task, this_cpu) != current ||
- !rt_task(current)) {
- per_cpu(prev_task, this_cpu) = current;
- per_cpu(task_counter, this_cpu) = 0;
- }
- else if ((++per_cpu(task_counter, this_cpu) > 10) && printk_ratelimit()) {
-
- spin_lock(&print_lock);
- printk(KERN_ERR "BUG: possible soft lockup detected on CPU#%u! %lu-%lu(%lu)\n",
- this_cpu, jiffies, timestamp, timeout);
- printk("curr=%s:%d\n",current->comm,current->pid);
-
- dump_stack();
+ if (current->pid) {
+ if (++current->softlockup_count > 10) {
+ spin_lock(&print_lock);
+ printk(KERN_ERR "BUG: possible soft lockup detected on CPU#%u! %lu-%lu(%lu)\n",
+ this_cpu, jiffies, timestamp, timeout);
+ printk("curr=%s:%d count=%ld\n",current->comm,current->pid,
+ current->softlockup_count);
+ dump_stack();
#if defined(__i386__) && defined(CONFIG_SMP)
- nmi_show_all_regs();
+ nmi_show_all_regs();
#endif
- spin_unlock(&print_lock);
- per_cpu(task_counter, this_cpu) = 0;
+ spin_unlock(&print_lock);
+ touch_light_softlockup_watchdog();
+ }
}

wake_up_process(per_cpu(watchdog_task, this_cpu));
@@ -101,7 +104,6 @@
nmi_show_all_regs();
#endif
spin_unlock(&print_lock);
- per_cpu(task_counter, this_cpu) = 0;
}
}

Index: linux_realtime_ernie/include/linux/sched.h
===================================================================
--- linux_realtime_ernie/include/linux/sched.h (revision 266)
+++ linux_realtime_ernie/include/linux/sched.h (working copy)
@@ -307,6 +307,7 @@
extern void softlockup_tick(void);
extern void spawn_softlockup_task(void);
extern void touch_softlockup_watchdog(void);
+extern void touch_light_softlockup_watchdog(void);
#else
static inline void softlockup_tick(void)
{
@@ -317,6 +318,9 @@
static inline void touch_softlockup_watchdog(void)
{
}
+static inline void touch_light_softlockup_watchdog(void)
+{
+}
#endif

/* Attach to any functions which should be ignored in wchan output. */
@@ -898,6 +902,12 @@
#ifdef CONFIG_DEBUG_PREEMPT
int lock_count;
#endif
+#ifdef CONFIG_DETECT_SOFTLOCKUP
+ unsigned long softlockup_count; /* Count to keep track how long the
+ * thread is in the kernel without
+ * sleeping.
+ */
+#endif
/* realtime bits */
struct list_head delayed_put;
struct plist pi_waiters;