linux-kernel - Re: floppy.c soft lockup

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Message-ID: <20070601183642.GA92@tv-sign.ru>
Date:	Fri, 1 Jun 2007 22:36:42 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Mark Hounschell <dmarkh@....rr.com>
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

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?

Oleg.

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