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    SubjectRe: [patch] Real-Time Preemption, -RT-2.6.9-mm1-V0

    * Ingo Molnar <mingo@elte.hu> wrote:

    > > Oct 26 21:43:56 porky kernel: BUG: sleeping function called from
    > > invalid context amlat(3963) at kernel/mutex.c:28
    > > Oct 26 21:43:56 porky kernel: in_atomic():1 [00000001], irqs_disabled():1
    > > Oct 26 21:43:56 porky kernel: [<c011c7da>] __might_sleep+0xca/0xe0 (12)
    > > Oct 26 21:43:56 porky kernel: [<c0137d89>] _mutex_lock+0x39/0x50 (36)
    > > Oct 26 21:43:56 porky kernel: [<c0137df6>] _mutex_lock_irqsave+0x16/0x20 (24)
    > > Oct 26 21:43:56 porky kernel: [<c012977d>] __mod_timer+0x4d/0x1f0 (12)
    > > Oct 26 21:43:56 porky kernel: [<c01f6535>] rtc_do_ioctl+0x185/0x970 (44)
    >
    > does the quick hack below help?

    here's a more complete fix.

    Ingo

    --- linux/drivers/char/rtc.c.orig
    +++ linux/drivers/char/rtc.c
    @@ -177,7 +177,7 @@ static unsigned long rtc_max_user_freq =
    /*
    * rtc_task_lock nests inside rtc_lock.
    */
    -static DECLARE_SPINLOCK(rtc_task_lock);
    +static DECLARE_RAW_SPINLOCK(rtc_task_lock);
    static rtc_task_t *rtc_callback = NULL;
    #endif

    @@ -238,10 +238,17 @@ irqreturn_t rtc_interrupt(int irq, void
    rtc_irq_data |= (CMOS_READ(RTC_INTR_FLAGS) & 0xF0);
    }

    - if (rtc_status & RTC_TIMER_ON)
    + if (rtc_status & RTC_TIMER_ON) {
    + spin_unlock (&rtc_lock);
    + /*
    + * We do the mod_timer outside of the lock because
    + * it may reschedule under PREEMPT_REALTIME. As long
    + * as we read the flag race-free it is not a problem
    + * if two mod_timer()s race:
    + */
    mod_timer(&rtc_irq_timer, jiffies + HZ/rtc_freq + 2*HZ/100);
    -
    - spin_unlock (&rtc_lock);
    + } else
    + spin_unlock (&rtc_lock);

    /* Now do the rest of the actions */
    spin_lock(&rtc_task_lock);
    @@ -1094,17 +1101,19 @@ static void rtc_dropped_irq(unsigned lon
    return;
    }

    - /* Just in case someone disabled the timer from behind our back... */
    - if (rtc_status & RTC_TIMER_ON)
    - mod_timer(&rtc_irq_timer, jiffies + HZ/rtc_freq + 2*HZ/100);
    -
    rtc_irq_data += ((rtc_freq/HZ)<<8);
    rtc_irq_data &= ~0xff;
    rtc_irq_data |= (CMOS_READ(RTC_INTR_FLAGS) & 0xF0); /* restart */

    freq = rtc_freq;

    - spin_unlock_irq(&rtc_lock);
    + /* Just in case someone disabled the timer from behind our back... */
    + if (rtc_status & RTC_TIMER_ON) {
    + spin_unlock_irq(&rtc_lock);
    + mod_timer(&rtc_irq_timer, jiffies + HZ/rtc_freq + 2*HZ/100);
    + } else
    + spin_unlock_irq(&rtc_lock);
    +

    printk(KERN_WARNING "rtc: lost some interrupts at %ldHz.\n", freq);

    -
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