linux-kernel - Re: [PATCH] PHYLIB: IRQ event workqueue handling fixes

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Message-ID: <Pine.LNX.4.64N.0710161759050.22596@blysk.ds.pg.gda.pl>
Date:	Tue, 16 Oct 2007 18:19:32 +0100 (BST)
From:	"Maciej W. Rozycki" <macro@...ux-mips.org>
To:	Jarek Poplawski <jarkao2@...pl>
cc:	Andy Fleming <afleming@...escale.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jeff Garzik <jgarzik@...ox.com>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PHYLIB: IRQ event workqueue handling fixes

On Tue, 16 Oct 2007, Jarek Poplawski wrote:

> Yes, it's all right here. Sorry for bothering - I should've found this
> by myself.

 Ah, no problem -- even with the right keys you may sometimes get lost in 
the results.

> I've still some doubts about this possible enable_irq() after
> free_irq(). If it's the only handler the status would be changed again
> and at least some of this code in check_irq_resend() would be run, but
> I can miss something again or/and this doesn't matter, as well.

 Well, enable_irq() and disable_irq() themselves are nesting, so they are 
not a problem.  OTOH, free_irq() does not seem to maintain the depth count 
correctly, which looks like a bug to me and which could trigger regardless 
of whether flush_scheduled_work() or cancel_work_sync() was called.

 The reason is CONFIG_DEBUG_SHIRQ which makes a simulated interrupt event 
be sent at the end of free_irq().  It looks like a problem that is 
complementary to one I signalled here:

http://lkml.org/lkml/2007/9/12/82

with respect to request_irq(), where, similarly, such an interrupt event 
is sent at the beginning.  It looks like nobody was concerned back then, 
but perhaps it is time to do a better investigation now and propose a 
solution.

 I'll think about it and thanks for your inquisitiveness that has led to 
these conclusions.

  Maciej
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