linux-kernel - Re: [RFC] genirq: Flush the irq thread on synchronization

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Message-ID: <alpine.LFD.2.02.1112070140340.2735@ionos>
Date:	Wed, 7 Dec 2011 01:48:30 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Ido Yariv <ido@...ery.com>
cc:	linux-kernel@...r.kernel.org
Subject: Re: [RFC] genirq: Flush the irq thread on synchronization

On Wed, 7 Dec 2011, Ido Yariv wrote:

> Hi Thomas,
> 
> On Mon, Dec 05, 2011 at 10:55:01PM +0100, Thomas Gleixner wrote:
> > Does the following (untested) patch solve your issues?
> 
> I briefly tested this patch and it appears to also solve the issues I
> mentioned.
> 
> I think both solutions would work. The only drawbacks I see in using
> this patch over the other one are that this patch involves a bit more
> locking in synchronize_irq() and irq_finalize_oneshot() (for non-oneshot
> irqs), and that the oneshot mechanism is used for non-oneshot threads.

I don't care about synchronize_irq() at all. It's a slow path anyway.

The extra burden in irq_finalize_oneshot() is somewhat of a concern,
but that locks should be completely uncontended for real threaded irq
users, so in practice it's a non issue.

It's the only solution which actually solves the thread_active leak,
though I just discovered a very narrow race window between the
test_and_clear_bit and the active increment, which is easy to
fix. I'll send out another version tomorrow

Thanks,

	tglx
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