linux-kernel - Re: floppy.c soft lockup

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Message-ID: <466078FF.2080508@cfl.rr.com>
Date:	Fri, 01 Jun 2007 15:52:31 -0400
From:	Mark Hounschell <dmarkh@....rr.com>
To:	Oleg Nesterov <oleg@...sign.ru>
CC:	Mark Hounschell <markh@...pro.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>
Subject: Re: floppy.c soft lockup

Oleg Nesterov wrote:
> On 06/01, Mark Hounschell wrote:
>> Oleg Nesterov wrote:
>>> Could you apply the trivial patch below, and change the i/o thread to do
>>>
>>> 		prctl(1234);				// hangs ???
>>> 		printf(something);
>>> 		ioctl(Q->DevSpec1, FDSETPRM, &medprm);	// this hangs
>>>
>>> to see if prctl() hangs or not? This way we can narrow the problem.
>>> (of course, you can just kill the above ioctl() if this is possible).
>>>
>>> Thanks!
>>>
>>> Oleg.
>>>
>>> --- OLD/kernel/sys.c~	2007-04-03 13:05:02.000000000 +0400
>>> +++ OLD/kernel/sys.c	2007-06-01 18:56:22.000000000 +0400
>>> @@ -2147,6 +2147,11 @@ asmlinkage long sys_prctl(int option, un
>>>  {
>>>  	long error;
>>>  
>>> +	if (option == 1234) {
>>> +		flush_scheduled_work();
>>> +		return 0;
>>> +	}
>>> +
>>>  	error = security_task_prctl(option, arg2, arg3, arg4, arg5);
>>>  	if (error)
>>>  		return error;
>>>
>>> -
>>
>> Ok the prctl never returned. I just replaced the ioctl with it and added
>> a printf before and after. I only get the one before. The thread is hung
>> at this point just as if I'd done the ioctl?
> 
> Thanks. So we can rule out floppy.c. flush_scheduled_work/flush_workqueue
> is broken by this RT application. Imho, this is not the kernel problem.
> 
> Now I am very sure that the initial suspect was correct: cpu starvation.
> I can cook a debug patch to be 100% sure tomorrow, which kernel version is
> most convenient to you?
> 

2.6.22-rc3 is fine thanks.

Regards
Mark

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