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

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Date:	Fri, 19 Oct 2007 13:57:33 +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 Fri, 19 Oct 2007, Jarek Poplawski wrote:

> But then... your patch seems to make it possible, because it enables
> irq to the initial state of the counter. Of course, this could happen
> on closing only.

 That's because free_irq() does not disable the interrupt in the correct 
manner.  The scenario is more or less like this:

phy_interrupt()				[depth == 0]
	disable_irq()
		depth++; status |= IRQ_DISABLED;
...
free_irq()				[depth == 1]
	status |= IRQ_DISABLED;
...
phy_change()				[depth == 1]
	enable_irq()
		depth--; status &= ~IRQ_DISABLED;
		oops!

Now if free_irq() correctly incremented the depth counter, then the last
enable_irq() would still decrement it, but with its initial value of 2 it 
would not change the status to reenable the line.

  Maciej
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