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

From: Steven Rostedt (rostedt_at_goodmis.org)
Date: 08/03/05

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    To: Ingo Molnar <mingo@elte.hu>
Date:	Wed, 03 Aug 2005 12:44:07 -0400

    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;

    -
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