linux-kernel - Re: lockdep and threaded IRQs (was: ...)

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Message-Id: <1236032722.5330.1675.camel@laptop>
Date:	Mon, 02 Mar 2009 23:25:22 +0100
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	David Brownell <david-b@...bell.net>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, me@...ipebalbi.com,
	linux-kernel@...r.kernel.org, linux-input@...r.kernel.org,
	felipe.balbi@...ia.com, dmitry.torokhov@...il.com,
	sameo@...nedhand.com, tglx@...utronix.de
Subject: Re: lockdep and threaded IRQs (was: ...)

On Mon, 2009-03-02 at 14:10 -0800, David Brownell wrote:

> What's unfortunate is that you prefer not to fix that
> IRQF_DISABLED bug in lockdep, which you co-"maintain".
> When running with lockdep, that bug (a) introduces bugs
> in some drivers and (b) hides bugs in others.  You've
> rejected even a minimal warning fix, to help minimize
> the amount of time developers waste on (a) and (b).

I've come to the conclusion that the only technically sound solution is
to do as I proposed today, utterly eliminate !IRQF_DISABLED handlers.

Apparently you had enough time to come up with the creative genirq abuse
of twl4030, I think that with a similar effort you could have
implemented generic threaded irq stuff like proposed by Thomas.

> Attacking folk for having to cope with such bugs escalates
> things beyond "unfortunate".  If lockdep is "maintained",
> your response should be fixing that lockdep bug.  Once
> that's done, all workarounds for that bug can be removed.

I state there is no lockdep bug in this respect. The bug is trying to
enable interrupts from hardirq context and running code that assumes
hardirq context from task context.

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