linux-kernel - Re: PPS parport boot lockup: INFO: HARDIRQ-READ-safe -> HARDIRQ-READ-unsafe lock order detected

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Date:	Mon, 24 Jan 2011 18:00:57 +0300
From:	Alexander Gordeev <lasaine@....cs.msu.su>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: PPS parport boot lockup: INFO: HARDIRQ-READ-safe ->
 HARDIRQ-READ-unsafe lock order detected

В Fri, 21 Jan 2011 08:37:34 -0800
Linus Torvalds <torvalds@...ux-foundation.org> пишет:

> On Fri, Jan 21, 2011 at 6:44 AM, Alexander Gordeev
> <lasaine@....cs.msu.su> wrote:
> >
> > But parport_unregister_device should probably never be called while
> > parport interrupts are enabled (in hardware). So this is a false
> > positive. Is this right?
> 
> "Enabled in hardware" is immaterial - with shared interrupts, it
> doesn't matter one whit whether parport interrupts are disabled on the
> chip, because some other chip may be using the same interrupt line.
> 
> So you'd need to have something that guarantees that there is no
> concurrent use, like actually unregistering the irq handler itself.
> Things like that can work.
> 
> HOWEVER, even then I think you should see the lockdep message as a
> problem. The automated toolchain is great because it shows problems
> that it thinks might happen - not when they happen, but based on a
> simpler theoretical model. Ignoring the error because there is some
> rule in place that is hard to explain to the automated toolchain is
> the wrong thing to do, because it makes the lockdep automation less
> reliable.
> 
> Think of it as a compiler warning - maybe the warning doesn't actually
> imply an actual bug, but you should strive to write code that doesn't
> warn, because otherwise the noise from the warning you ignored will
> make it harder for others to see the _real_ bugs.
> 
>                  Linus


Ok, thank you very much for clarification!
I'll send the patch as reply to the first e-mail.

-- 
  Alexander

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