linux-kernel - Re: [PATCH] genirq: Fix bad IRQ

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Date:	Sat, 19 Sep 2015 22:24:15 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Kohji Okuno <okuno.kohji@...panasonic.com>
cc:	marc.zyngier@....com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] genirq: Fix bad IRQ_ONSHOT in forced IRQ setting

On Sun, 20 Sep 2015, Kohji Okuno wrote:
> From: Thomas Gleixner <tglx@...utronix.de>
> Date: Fri, 18 Sep 2015 16:46:24 +0200
> > On Fri, 18 Sep 2015, Kohji Okuno wrote:
> >> 
> >> irq thread(runs sdhci_thread_irq()) is waiting on
> >> drivers/mmc/core/core.c:mmc_wait_for_req_done() in order to access
> >> a SDIO register. And, this thread shoud be woken up from
> >> sdhci_irq() after the completion of the register access.
> >> But, since the IRQ is masked, sdhci_irq() is not called and  irq
> >> thread can not wake up. This is root cause, I think.
> >> What do you think about this?
> > 
> > Ah, that explains it. Let me think about it a bit.
> 
> If something is not clear please let me know.
> By the way, even if other issue exists, we should change
> irq_setup_forced_threading() as my patch, I think.

No, we can't. We can only do that if the interrupt is not shared.

Assume the following scenario:

       request_irq(irq, handler, IRQF_SHARED, "devA", devidA);

In case of force threading that sets the oneshot flag for the irq
descriptor.

Now the sdhci driver is initialized

       request_thread_irq(irq, handler, thandler, IRQF_SHARED,
       			  "sdhci", devidSDHCI);

The oneshot flag sticks and you run into exactly the same issue as
now.

Shared interrupts are a major pain, but we have to deal with them.

I'm working on a solution for that issue.

Thanks,

	tglx
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