Re: 2.6.15-rc5-rt4: BUG: swapper:0 task might have lost a preemption check!

["K.R. Foley" <kr@cybsft.com>]

Steven Rostedt wrote:
> On Thu, 2005-12-22 at 21:14 -0600, K.R. Foley wrote:
>> Lee Revell wrote:
>>> Got this on boot.  Same .config as the last one I sent you.
>>>
>>> VP_IDE: VIA vt8235 (rev 00) IDE UDMA133 controller on pci0000:00:11.1
>>>     ide1: BM-DMA at 0xe008-0xe00f, BIOS settings: hdc:DMA, hdd:pio
>>> Probing IDE interface ide1...
>>> BUG: swapper:0 task might have lost a preemption check!
>>>  [<c010440c>] dump_stack+0x1c/0x20 (20)
>>>  [<c01166aa>] preempt_enable_no_resched+0x5a/0x60 (20)
>>>  [<c0100dd9>] cpu_idle+0x79/0xb0 (12)
>>>  [<c0100280>] _stext+0x40/0x50 (28)
>>>  [<c03078e6>] start_kernel+0x176/0x1d0 (20)
>>>  [<c0100199>] 0xc0100199 (1086889999)
>>> ---------------------------
>>> | preempt count: 00000000 ]
>>> | 0-level deep critical section nesting:
>>> ----------------------------------------
>>>
>>>
> 
> 
> OK, I just found an SMP bug, and here's the patch.  Maybe this will help
> you kr.  I'm currently running x86_64 SMP with 2.6.15-rc5-rt4 with this
> and my softirq-no-hrtimers patch I sent earlier.
> 
> -- Steve
> 
> Index: linux-2.6.15-rc5-rt4/kernel/workqueue.c
> ===================================================================
> --- linux-2.6.15-rc5-rt4.orig/kernel/workqueue.c	2005-12-23 10:23:25.000000000 -0500
> +++ linux-2.6.15-rc5-rt4/kernel/workqueue.c	2005-12-23 10:25:21.000000000 -0500
> @@ -370,10 +370,17 @@
>  void set_workqueue_thread_prio(struct workqueue_struct *wq, int cpu,
>  				int policy, int rt_priority, int nice)
>  {
> -	struct task_struct *p = wq->cpu_wq[cpu].thread;
> +	struct cpu_workqueue_struct *cwq;
> +	struct task_struct *p;
>  	struct sched_param param = { .sched_priority = rt_priority };
> +	unsigned long flags;
>  	int ret;
>  
> +	cwq = per_cpu_ptr(wq->cpu_wq, cpu);
> +	spin_lock_irqsave(&cwq->lock, flags);
> +	p = cwq->thread;
> +	spin_unlock_irqrestore(&cwq->lock, flags);
> +
>  	set_user_nice(p, nice);
>  	ret = sys_sched_setscheduler(p->pid, policy, &param);
>  	if (ret)
> 
> 
> 

OK. The BUG still exists (output below) but it does boot now with the
above patch applied (THANKS Steven!), which would seem to imply the two
weren't related. ARGH! :)

Dec 23 10:16:27 porky kernel: Event source lapic installed with caps set: 06
Dec 23 10:16:27 porky kernel: BUG: swapper:0 task might have lost a
preemption check!
Dec 23 10:16:27 porky kernel: Brought up 2 CPUs
Dec 23 10:16:27 porky kernel: checking if image is initramfs... it is
Dec 23 10:16:27 porky kernel:  [<c010424e>] dump_stack+0x1e/0x20 (20)
Dec 23 10:16:27 porky kernel:  [<c011c9cf>]
preempt_enable_no_resched+0x5f/0x70 (20)
Dec 23 10:16:27 porky kernel:  [<c0100ff2>] cpu_idle+0xb2/0x100 (40)
Dec 23 10:16:27 porky kernel:  [<c0111446>]
start_secondary+0x296/0x340<6>Freeing initrd memory: 452k freed


-- 
   kr