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

[Alexander Gordeev]

Ð Fri, 21 Jan 2011 08:37:34 -0800
Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> ÐÐÑÐÑ:

> On Fri, Jan 21, 2011 at 6:44 AM, Alexander Gordeev
> <lasaine@xxxxxxxxxxxxx> 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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