linux-kernel - Re: [PATCH v2] genirq: Check irq disabled & masked states in irq

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Date:   Sat, 27 May 2017 10:30:51 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Jeffy Chen <jeffy.chen@...k-chips.com>
cc:     linux-kernel@...r.kernel.org, briannorris@...omium.org,
        dianders@...omium.org, tfiga@...omium.org
Subject: Re: [PATCH v2] genirq: Check irq disabled & masked states in
 irq_shutdown

On Sat, 27 May 2017, Jeffy Chen wrote:

> If a irq is already disabled & masked, free_irq may cause a unbalanced
> irq shutdown/disable/mask, for example:

No, it's not. irq_shutdown/disable/mask are low level access functions
which can be invoked at any given time.

The only interface which has refcounting is disable/enable_irq().

> devm_request_irq->irq_startup->irq_enable
> disable_irq					<-- disabled and masked
> devm_free_irq->irq_shutdown			<-- try to disable it again
> 
> This would confuse some pinctrl drivers which would control clk in
> irq_enable/irq_disable, for example pinctrl-rockchip/pinctrl-nomadik.
>
> This patch add a state check in irq_shutdown to prevent that.

Please read Documentation/process/SubmittingPatches and search for "this
patch".

> diff --git a/kernel/irq/chip.c b/kernel/irq/chip.c
> index 686be4b..816da03 100644
> --- a/kernel/irq/chip.c
> +++ b/kernel/irq/chip.c
> @@ -206,14 +206,20 @@ int irq_startup(struct irq_desc *desc, bool resend)
>  
>  void irq_shutdown(struct irq_desc *desc)
>  {
> -	irq_state_set_disabled(desc);
>  	desc->depth = 1;
> +
> +	if (unlikely(irqd_irq_disabled(&desc->irq_data) &&
> +		irqd_irq_masked(&desc->irq_data)))
> +		goto out;

This is just wrong.

It's perfectly legit to call disable_irq() and then free_irq(). Still
free_irq() has to be able to invoke chip->irq_shutdown(). Preventing that
will leave some interrupt chips in a half initialized state.

The irq core does not guarntee that the unmask/mask enable/disable
startup/shutdown callbacks are perfectly balanced. irq_shutdown() is only
one place where this can happen. This needs more thought than this 'works
for me' hackery.

Thanks,

	tglx