linux-kernel - Re: lockdep and threaded IRQs

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Message-ID: <49A92487.3020108@s5r6.in-berlin.de>
Date:	Sat, 28 Feb 2009 12:48:23 +0100
From:	Stefan Richter <stefanr@...6.in-berlin.de>
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, a.p.zijlstra@...llo.nl, tglx@...utronix.de
Subject: Re: lockdep and threaded IRQs

David Brownell wrote:
> Now, where is that being set up as being threaded?  I
> referenced that a message or two earlier:
> 
>   drivers/mfd/twl4030-irq.c
> 
> Where you'll observe twl_init_irq() at line 688 setting
> up the thread and the Primary IRQ Handler (PIH) dispatch.
> That's pretty much bog-standard chained IRQ setup code,
> except that it chains through a thread.
> 
> When an IRQ comes in, handle_twl4030_pih() acks and masks
> that top level IRQ.  Then it wakes twl4030_irq_thread(),
> which issues I2C operations to read the IRQ status from
> the chip ... first PIH to find out which SIH modules are
> raising an IRQ, then SIH to dispatch that status.  Then
> handle_irq() from that thread to invoke the handler in
> that thread context; it will issue more I2C ops.
> 
> And the lockdep thing kicks in through handle_irq(),
> where the IRQ handler wrongly gets invoked with the
> IRQs disabled -- iff lockdep is enabled.  Otherwise,
> that IRQ thread is just like any other thread.

Ah, so there /is/ a threaded IRQ handler implementation in the mainline,
down in some driver framework...

Why don't these drivers simply use <linux/workqueue.h>?
-- 
Stefan Richter
-=====-==--= --=- ===--
http://arcgraph.de/sr/
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