linux-kernel - Re: [BUG] irq_dispose_mapping after irq request failure

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Message-ID: <1360630273.2035.2.camel@pasglop>
Date:	Tue, 12 Feb 2013 11:51:13 +1100
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Grant Likely <grant.likely@...retlab.ca>
Cc:	Michael Ellerman <michael@...erman.id.au>,
	Baruch Siach <baruch@...s.co.il>,
	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [BUG] irq_dispose_mapping after irq request failure

On Mon, 2013-02-11 at 20:52 +0000, Grant Likely wrote:
> Really the irq mappings should be using reference counting. The existing
> code is naive on this count and just releases the irq on the first call
> to irq_dispose_mapping().  I've not gotten around to fixing that. Anyone
> want to take that task on?

Is this the best approach ?

The original idea was that there was no point disposing of mappings in most
cases and keeping the mapping around would provide a bit of stability of
interrupt numbers which might come in handy for debugging etc...

The few cases where disposing of a mapping might be useful is if the underlying
physical interrupts completely disappear, as in a cascaded controller gets
removed or that sort of thing, which is a very rare case... And even then...

Could you just make irq_dispose_mapping() check if the irq desc is
active and fail/WARN/BUG if it is ? I don't see the point of adding a refcount,
that feels overkill.

Cheers,
Ben.

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