linux-kernel - Re: [PATCH] uio: fix devm_request

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Message-ID: <20131220180113.GF2881@blackmetal.musicnaut.iki.fi>
Date:	Fri, 20 Dec 2013 20:01:13 +0200
From:	Aaro Koskinen <aaro.koskinen@....fi>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Aaro Koskinen <aaro.koskinen@....com>,
	"Hans J. Koch" <hjk@...sjkoch.de>, linux-kernel@...r.kernel.org,
	Michal Simek <michal.simek@...inx.com>
Subject: Re: [PATCH] uio: fix devm_request_irq usage

Hi,

On Fri, Dec 20, 2013 at 08:49:13AM -0800, Greg Kroah-Hartman wrote:
> On Fri, Dec 20, 2013 at 04:19:47PM +0200, Aaro Koskinen wrote:
> > Commit e6789cd3dfb553077606ccafeb05e0043f072481 (uio: Simplify uio error
> > path by using devres functions) converted uio to use devm_request_irq().
> > This introduced a change in behaviour since the IRQ is associated with
> > the parent device instead of the created UIO device. The IRQ will remain
> > active after uio_unregister_device() is called, and some drivers will
> > crash because of this. The patch fixes this.
> 
> What drivers crash because of this?  Any in-kernel drivers?

I saw a crash with Intel DPDK (http://www.dpdk.org/) igb_uio
driver. Basically, they do:

	uio_unregister_device
	pci_disable_msix <-- this will BUG() if there is an active IRQ

I cannot test any of the in-tree UIO drivers, but at least some
of them seem to release resources the IRQ handler might use after
uio_unregister_device(). So if the IRQ fires results would not probably
be very good.

A.
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