linux-kernel - Re: [BUG] genirq: Race condition in ONESHOT IRQ handler disabling IRQ forever

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Date:	Tue, 7 Feb 2012 11:01:06 +0100
From:	Lothar Waßmann <LW@...O-electronics.de>
To:	Yong Zhang <yong.zhang0@...il.com>
Cc:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [BUG] genirq: Race condition in ONESHOT IRQ handler disabling
 IRQ forever

Hi,

> On Mon, Feb 06, 2012 at 09:14:47AM +0100, Lothar Waßmann wrote:
> > Hi,
> > 
> > I already sent this to <linux-kernel@...r.kernel.org> on Feb. 1, 2012
> > but did not get any response there. So resending to a wider audience
> > with improved subject line:
> > 
> > there is a race condition in the threaded IRQ handler code for oneshot
> > interrupts that may lead to disabling an IRQ indefinitely. IRQs are
> > masked before calling the hard-irq handler and are unmasked only after
> > the soft-irq handler has been run. Thus if the hard-irq handler
> > returns IRQ_HANDLED instead of IRQ_WAKE_THREAD, meaning the soft-irq
> > will not be called, the interrupt will remain masked forever.
> > 
> > This can happen due to a short pulse on the interrupt line, that
> > triggers the interrupt logic, but goes undetected by the hard-irq
> > handler. The problem can be reproduced with the TSC2007 touch
> > controller driver that uses ONESHOT interrupts.
> 
> Isn't it the responsibility of the driver (say TSC2007)?
> 
> In this case, TSC2007 should return IRQ_WAKE_THREAD IMHO.
> 
That would mean it had to return IRQ_WAKE_THREAD unconditionally
making the return code useless.
And it would cause an extra useless loop through the softirq
handler.


Lothar Waßmann
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