linux-kernel - Re: Linux 3.4 released

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Date:	Tue, 22 May 2012 20:26:04 +0200
From:	Jörg-Volker Peetz <jvpeetz@....de>
To:	linux-kernel@...r.kernel.org
Subject: Re: Linux 3.4 released

Tejun Heo wrote, on 05/22/12 19:03:
> On Tue, May 22, 2012 at 06:52:49PM +0200, Jörg-Volker Peetz wrote:
>> I tried the above patch but was not able to see a line beginning with "XXX", not
>> on the text-console nor in any log-file. After the hard-lock, I can see only the
>> console-screen which now changed slightly:
>>
>> BUG: Unable to handle kernel NULL pointer dereference at 0000000000000008
>> IP: [<ffffffff8103ed60>] delayed_work_timer_fn+0x30/0x60
> 
> Oh, &cwq->wq is at offset 8 so cwq should have been -8.  Maybe I'm
> just confused.  Can you please try the following instead?
> 
> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> index 5abf42f..14babfe 100644
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -1096,10 +1096,16 @@ queue_work_on(int cpu, struct workqueue_struct *wq, struct work_struct *work)
>  }
>  EXPORT_SYMBOL_GPL(queue_work_on);
>  
> +#include <linux/uaccess.h>
>  static void delayed_work_timer_fn(unsigned long __data)
>  {
>  	struct delayed_work *dwork = (struct delayed_work *)__data;
>  	struct cpu_workqueue_struct *cwq = get_work_cwq(&dwork->work);
> +	unsigned long v;
> +
> +	if (probe_kernel_read(&v, &cwq->wq, sizeof(v)))
> +		printk("XXX delayed_work_timer_fn: cwq %p, fn=%pf\n",
> +		       cwq, dwork->work.func);
>  
>  	__queue_work(smp_processor_id(), cwq->wq, &dwork->work);
>  }

Also with this second patch I wasn't able to see any output beginning with "XXX
delayed_work_timer_fn:". It should appear in the system log or on the text-console?

The screen dump starts with:

BUG: Unable to handle kernel NULL pointer dereference at 0000000000000008
IP: [<ffffffff........>] delayed_work_timer_fn+0x31/0x70

I didn't find the time to type more. Or did I miss the essential?
-- 
Best regards,
Jörg-Volker.

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