linux-kernel - Re: [PATCH] KVM: Use IRQF_ONESHOT for assigned device MSI interrupts

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Date:	Mon, 04 Jun 2012 15:16:33 +0200
From:	Jan Kiszka <jan.kiszka@...mens.com>
To:	Thomas Gleixner <tglx@...utronix.de>
CC:	Avi Kivity <avi@...hat.com>,
	Alex Williamson <alex.williamson@...hat.com>,
	"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
	"mtosatti@...hat.com" <mtosatti@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"yongjie.ren@...el.com" <yongjie.ren@...el.com>
Subject: Re: [PATCH] KVM: Use IRQF_ONESHOT for assigned device MSI interrupts

On 2012-06-04 15:07, Thomas Gleixner wrote:
> On Mon, 4 Jun 2012, Jan Kiszka wrote:
>> On 2012-06-04 13:21, Thomas Gleixner wrote:
>> So this shortcut requires some checks before being applied to a specific
>> MSI/MSI-X vector.
>>
>>
>> Taking KVM aside, my general question remains if threaded MSI handlers
>> of all devices really need to apply IRQF_ONESHOT though they should have
>> no use for it.
> 
> In theory no, but we had more than one incident, where threaded irqs
> w/o a primary handler and w/o IRQF_ONEHSOT lead to full system
> starvation. Linus requested this sanity check and I think it's sane
> and required.

OK.

> 
> In fact it's a non issue for MSI. MSI uses handle_edge_irq which does
> not mask the interrupt. IRQF_ONESHOT is a noop for that flow handler.

Isn't irq_finalize_oneshot processes for all flows?

Jan

-- 
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux
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