linux-kernel - Re: 2.6.21-rc7-mm2 "irqpoll" seems to be broken

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Message-ID: <20070508171841.GA29733@in.ibm.com>
Date:	Tue, 8 May 2007 22:48:41 +0530
From:	Vivek Goyal <vgoyal@...ibm.com>
To:	Bernhard Walle <bwalle@...e.de>
Cc:	Morton Andrew Morton <akpm@...ux-foundation.org>,
	linux kernel mailing list <linux-kernel@...r.kernel.org>
Subject: Re: 2.6.21-rc7-mm2 "irqpoll" seems to be broken

On Thu, May 03, 2007 at 12:19:32AM +0200, Bernhard Walle wrote:
> * Vivek Goyal <vgoyal@...ibm.com> [2007-04-30 10:48]:
> > 
> > handle_edge_irq() already makes sure that desc->action is not null, still
> > note_interrupt() is receiving desc->action as null, that's strange. On my 
> > system this is happening for irq 4 and /proc/interrupt shows that it is
> > coming from "serial".
> 
> Unfortunately, I couldn't reproduce this here. Vivek, do you have time
> to take a look at this at your site? For the meanwhile, should I
> create a patch that checks for desc->action in note_interrupt(), too?
> 

Hi Bernhard,

I can reproduce this problem only on one machine. I think there is some
race condition and your code somehow just exposes it.

I put few WARN_ON(!desc->action) in handle_edge_irq() and what I find
that after handle_IRQ_event(), desc->action has become null. That means
in the meantime somebody has gone ahead and modified the desc. This must
have happened because we have release desc->lock while running
handle_IRQ_event().

This means there is a race somewhere. It is verified by the fact that
this problem does not occur if same system is booted with only one
cpu (maxcpus=1).

Thanks
Vivek
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