linux-kernel - Re: [PATCH v1 3/4] spi/xilinx: Simplify irq allocation

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Message-ID: <20130708162642.GM27646@sirena.org.uk>
Date:	Mon, 8 Jul 2013 17:26:42 +0100
From:	Mark Brown <broonie@...nel.org>
To:	Michal Simek <monstr@...str.eu>
Cc:	Michal Simek <michal.simek@...inx.com>,
	linux-kernel@...r.kernel.org,
	linux-spi <linux-spi@...r.kernel.org>,
	Grant Likely <grant.likely@...aro.org>,
	spi-devel-general@...ts.sourceforge.net
Subject: Re: [PATCH v1 3/4] spi/xilinx: Simplify irq allocation

On Mon, Jul 08, 2013 at 05:48:14PM +0200, Michal Simek wrote:
> On 07/08/2013 04:49 PM, Mark Brown wrote:

> > Is it definitely safe to leave the IRQ hanging around after the master
> > has been freed - there's no possibility of a late error interrupt or
> > something?

> I think it is more generic question if this race condition is fine
> for all drivers which are using devres groups.

Well, it's mainly an issue for IRQs - the other resources don't initiate
events by themselves which is what causes the issue.  It just needs a
bit of extra care so I wanted to check that this has been thought of.

> I have just looked at it and devres_release_all() is called where
> driver is unload and irq are disabled there.

The problem is the gap between the resources used to handle the IRQ
being freed and the IRQ itself being freed - if the hardware can be
guaranteed to be idle then that's fine but we need to be sure that is
OK.  Otherwise the interrupt handler may get run and be looking at a
resource which was freed which would be unfortunate.

> btw: What's the proper way for spi driver unregistration?

> spi_unregistered_master() (which also free private structure)
> and
> spi_master_put()?

Yes.

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