linux-kernel - Re: [BUG][PPC64] BUG in 2.6.26.5-rt9 causing Hang

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Date:	Mon, 29 Sep 2008 18:00:01 -0400
From:	Gregory Haskins <ghaskins@...ell.com>
To:	linux-rt-users <linux-rt-users@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Steven Rostedt <rostedt@...dmis.org>, chirag@...ux.vnet.ibm.com
CC:	dvhltc@...ibm.com
Subject: Re: [BUG][PPC64] BUG in 2.6.26.5-rt9 causing Hang

Gregory Haskins wrote:
> Gregory Haskins wrote:
>   
>> Hi Chirag
>>
>> Chirag Jog wrote:
>>   
>>     
>>> Hi Gregory,
>>> We see the following BUG followed by a hang on the latest kernel 2.6.26.5-rt9 on a Power6 blade (PPC64)
>>> It is easily recreated by running the async_handler or sbrk_mutex (realtime tests from ltp) tests.
>>>   
>>>     
>>>       
>> Call me an LTP newbie, but where can I get the sbrk_mutex/async_handler
>> tests.
>>     
> Ok, I figured out this part.  I needed a newer version of the .rpm from
> a different repo.  However, both async_handler and sbrk_mutex seem to
> segfault for me.  Hmm
>   

Thanks to help from Darren I got around this issue.  Unfortunately both
tests pass so I cannot reproduce this issue, nor do I see the problem
via code inspection.  Ill keep digging but I am currently at a loss.  I
may need to send you some diagnostic patches to find this, if that is ok
with you Chirag?

-Greg

> ---
>
> ghaskins@...t:~> uname -a
> Linux test 2.6.26.5-rt9-rt #1 SMP PREEMPT RT Mon Sep 29 14:26:45 EDT
> 2008 x86_64 x86_64 x86_64 GNU/Linux
>
> test:/home/ghaskins #
> /usr/lib64/ltp/testcases/realtime/func/async_handler/async_handler
>
> -----------------------------------
> Asynchronous Event Handling Latency
> -----------------------------------
>
> jvmsim disabled
> Running 1000000 iterations
> Segmentation fault
>
> ---
>
> Any ideas?
>
> -Greg
>
>   
>>   I installed the LTP rpm and I dont seem to have tests by that
>> name.  I have a 26.5-rt9 kernel all configured and ready to go but no
>> way to reproduce this issue.  Please advise.
>>
>> Regards,
>> -Greg
>>
>>
>>   
>>     
>>> login: cpu 0x2: Vector: 700 (Program Check) at [c0000000e8e875d0]
>>>     pc: c00000000005110c: .pick_next_pushable_task+0x54/0x9c
>>>     lr: c000000000059f50: .push_rt_task+0x44/0x2b4
>>>     sp: c0000000e8e87850
>>>    msr: 8000000000021032
>>>   current = 0xc0000000ea5bb2e0
>>>   paca    = 0xc000000000608700
>>>     pid   = 2811, comm = async_handler
>>> kernel BUG at kernel/sched_rt.c:1041! <---------------------
>>> enter ? for help
>>> [link register   ] c000000000059f50 .push_rt_task+0x44/0x2b4
>>> [c0000000e8e87850] c0000000e8e878f0 (unreliable)
>>> [c0000000e8e87900] c00000000005a1dc .push_rt_tasks+0x1c/0x38
>>> [c0000000e8e87980] c00000000005a21c .post_schedule_rt+0x24/0x44
>>> [c0000000e8e87a10] c000000000057cbc .finish_task_switch+0xd0/0x180
>>> [c0000000e8e87ab0] c0000000003b6e88 .__schedule+0x6e0/0x798
>>> [c0000000e8e87b90] c0000000003b7148 .schedule+0xec/0x11c
>>> [c0000000e8e87c10] c0000000003b7a40 .do_nanosleep+0x6c/0xcc
>>> [c0000000e8e87c90] c000000000080738 .hrtimer_nanosleep+0x7c/0x100
>>> [c0000000e8e87d90] c000000000080830 .sys_nanosleep+0x74/0x94
>>> [c0000000e8e87e30] c0000000000086ac syscall_exit+0x0/0x40
>>> --- Exception: c00 (System Call) at 0000008026449844
>>> SP (400014185f0) is in userspace
>>>
>>>
>>> This is generated by the BUG_ON lines in the pick_next_pushable function
>>> introduced by the sched-only-push-once-per-queue.patch .
>>>
>>> The -rt kernel prior to this patch didnot give such BUGes.
>>>
>>> All this was tried with
>>> CONFIG_GROUP_SCHED=N
>>> CONFIG_RT_GROUP_SCHED=N
>>>
>>>
>>> Setting the options
>>> CONFIG_GROUP_SCHED=y
>>> CONFIG_RT_GROUP_SCHED=Y,
>>> seems to solve the problem.
>>>
>>>
>>>
>>>   
>>>     
>>>       
>>   
>>     
>
>
>   



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