linux-kernel - RE: [PATCH] genirq: for edge interrupt IRQS

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Message-ID: <alpine.LFD.2.02.1210121440160.2779@ionos>
Date:	Fri, 12 Oct 2012 14:46:18 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	"Liu, Chuansheng" <chuansheng.liu@...el.com>
cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] genirq: for edge interrupt IRQS_ONESHOT support with
 irq thread

On Fri, 12 Oct 2012, Liu, Chuansheng wrote:
> > -----Original Message-----
> > From: Thomas Gleixner [mailto:tglx@...utronix.de]
> > Sent: Friday, October 12, 2012 8:32 PM
> > To: Liu, Chuansheng
> > Cc: linux-kernel@...r.kernel.org
> > Subject: Re: [PATCH] genirq: for edge interrupt IRQS_ONESHOT support with irq
> > thread
> > 
> > On Fri, 12 Oct 2012, Chuansheng Liu wrote:
> > >
> > > In our system, there is one edge interrupt, and we want it to be
> > > irq thread with IRQS_ONESHOT, and found in handle_edge_irq(),
> > > even with IRQS_ONESHOT, the irq is still unmasked without care of
> > > flag IRQS_ONESHOT.
> > >
> > > It causes IRQS_ONESHOT can not work well for edge interrupt, but also
> > > after the irq thread finished with flag IRQS_ONESHOT, the irq will be
> > > possible to be unmasked again, it should be messing mask/unmask logic.
> > 
> > This is just wrong. By masking edge interrupts you will run into
> > situations where you will lose interrupts.
> > 
> > Can you please explain, why you want to mask your edge interrupt?

> When I request_irq with irq thread handler and flag IRQS_ONESHOT, if
> do not mask the edge interrupt, the primary handler and irq thread
> maybe run at the same time, and in my real case it causes spin
> deadlock.

Then your code is simply wrong and you need to fix it instead of hacking a
workaround into the core code. Locking is not that hard.

> You means it is not right with IRQS_ONESHOT for edge interrupt?

It's wrong. Simnply because you can lose interrupts.

     interrupt raised
     	 handle_edge_irq()
	    mask_ack_irq()
	    handle_event()
	        wake irq thread
     reti

     irq thread runs
     	 handle device interrupt()
				   <--- device issues edge irq
	 unmask_irq()

This interrupt is not delivered. So your device stops working. Not
what you want, right?

Thanks,

	tglx
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