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

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Date:	Fri, 21 Jan 2011 20:43:17 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Alexander Gordeev <lasaine@....cs.msu.su>,
	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


* Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> 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.

Yeah. Also, inevitably the false positives have a higher likelyhood
of making it into a released kernel, often because the bugs where
there was a real lockup as well got noticed via other means.

It's similar with compiler warnings as well: the questionable ones where
GCC is wrong or at least confused accumulate.

Also note that here there's a real lockup here as well, shortly after the lockdep 
message - the boot never continues, the box keep spewing the PPS debug messages:

[   76.240020] pps pps0: PPS event at 4294911356
[   76.244380] pps pps0: PPS event at 1295471377.240018362
[   76.249608] pps pps0: capture assert seq #2
[   77.252019] pps pps0: PPS event at 4294911609
[   77.256379] pps pps0: PPS event at 1295471378.252017372
[   77.261604] pps pps0: capture assert seq #3
[   78.264021] pps pps0: PPS event at 4294911862
[   78.268387] pps pps0: PPS event at 1295471379.264018619
[   78.273621] pps pps0: capture assert seq #4
[   79.276018] pps pps0: PPS event at 4294912115
[   79.280384] pps pps0: PPS event at 1295471380.276016791
[   79.285619] pps pps0: capture assert seq #5

But nothing happens, the boot never continues.

Thanks,

	Ingo
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