linux-kernel - Re: [PATCH] genirq: Only call irq

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Message-ID: <alpine.DEB.2.11.1504211408300.13914@nanos>
Date:	Tue, 21 Apr 2015 14:20:22 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Adrian-Ken Rueegsegger <ken@...elabs.ch>
cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] genirq: Only call irq_ack if implemented by chip

On Wed, 15 Apr 2015, Adrian-Ken Rueegsegger wrote:
> To support PCI MSI(-X), we register our own platform-specific MSI
> operations (x86_msi.setup_msi_irqs, etc) and implement an irq_chip that
> simply provides the irq_mask and irq_unmask operations (by reusing the
> "regular" mask_msi_irq/unmask_msi_irq).

But why are you using the edge flow handler then? 

> After encountering a null pointer dereference due to the irq_chip not
> providing an irq_ack operation, I examined the commit that changed the
> source of the irq_ack call, noticing that only the check in
> handle_edge_irq was dropped while the other call sites were kept. As the
> commit message did not provide me with additional information for that
> particular fragment of the change, I (prematurely) concluded that it was
> not intentional.
> 
> If it is a prerequisite for IRQ chips to provide the irq_ack operation
> when used in conjunction with handle_edge_irq, then please ignore my
> patch. In that case, I will adjust our chip implementation
> accordingly.

Yes, it is more or less. And I really want to avoid the extra
conditional in the handler hotpath.

Thanks,

	
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