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

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Date:   Tue, 25 Oct 2016 11:45:55 +0100
From:   Marc Zyngier <marc.zyngier@....com>
To:     Mason <slash.tmp@...e.fr>, Sebastian Frias <sf84@...oste.net>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     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 25/10/16 09:36, Mason wrote:
> 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

One important difference between disable and mask is that disable is
perfectly allowed not to care about pending signals, whereas mask must
preserve an interrupt becoming pending whilst masked.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...