linux-kernel - RE: [PATCH] genirq: for edge interrupt IRQS

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Date:	Fri, 12 Oct 2012 22:53:56 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	"Liu, Chuansheng" <chuansheng.liu@...el.com>
cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] genirq: for edge interrupt IRQS_ONESHOT support with
 irq thread

On Fri, 12 Oct 2012, Liu, Chuansheng wrote:

> > On SMP an interrupt which is raised after the ack() again before the
> > handler finishes, can invoke another delivery on a different CPU,
> > which then sees the IRQ_INPROGESS flag, masks it and flags it
> > PENDING. When the primary handler on the first CPU returns, it sees
> > the PENDING flag, unmasks and invokes the handler another time.
> In this case, when IRQ_INPROGRESS flag is set, on another CPU, it will
> mask and ack it, if before the primary handler on the first CPU returns,
> the edge interrupt is raised again, it will be lost, right?
> So I think set PENDING just confirm one time, it just depends on primary handler
> execution time and irq frequency.

It does NOT matter. We marked it PENDING. And that guarantees that we
invoke the handler again after unmasking. And that keeps stuff rolling.

We would lose when we masked and did not notice that there was one,
but we notice and store that information with the PENDING flag.


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