linux-kernel - Re: Disabling an interrupt in the handler locks the system up

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Date:   Tue, 25 Oct 2016 10:36:34 +0200
From:   Mason <slash.tmp@...e.fr>
To:     Sebastian Frias <sf84@...oste.net>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     Marc Zyngier <marc.zyngier@....com>,
        Jason Cooper <jason@...edaemon.net>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: Disabling an interrupt in the handler locks the system up

On 25/10/2016 10:29, Sebastian Frias wrote:

> On 10/24/2016 06:55 PM, Thomas Gleixner wrote:
>
>> On Mon, 24 Oct 2016, Mason wrote:
>>
>>> For the record, setting the IRQ_DISABLE_UNLAZY flag for this device
>>> makes the system lock-up disappear.
>>
>> The way how lazy irq disabling works is:
>>
>> 1) Interrupt is marked disabled in software, but the hardware is not masked
>>
>> 2) If the interrupt fires befor the interrupt is reenabled, then it's
>>    masked at the hardware level in the low level interrupt flow handler.
> 
> Would you mind explaining what is the intention behind?
> Because it does not seem obvious why there isn't a direct map between
> "disable_irq*()" and "mask_irq()"

I had a similar, but slightly different question:

What is the difference between struct irq_chip's

 * @irq_shutdown:	shut down the interrupt (defaults to ->disable if NULL)
 * @irq_disable:	disable the interrupt
 * @irq_mask:		mask an interrupt source

(enable seems to default to unmask, but disable does not default to mask)

Regards.