linux-kernel - Re: [PATCH 2/3] HPET: Enter hpet_interrupt

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Message-ID: <s5htzafr07t.wl%tiwai@suse.de>
Date:	Mon, 10 Nov 2008 17:53:58 +0100
From:	Takashi Iwai <tiwai@...e.de>
To:	"Matt Fleming" <mjf@...too.org>
Cc:	"Will Newton" <will.newton@...il.com>,
	linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...e.hu,
	venkatesh.pallipadi@...el.com
Subject: Re: [PATCH 2/3] HPET: Enter hpet_interrupt_handler with interrupts disabled

At Sun, 2 Nov 2008 22:23:13 +0000,
Matt Fleming wrote:
> 
> 2008/11/2 Will Newton <will.newton@...il.com>:
> >
> > Combining IRQF_DISABLED and IRQF_SHARED does not reliably disable
> > interrupts in the handler. Perhaps IRQF_SHARED should be removed at
> > the same time?
> >
> 
> I didn't know that. Under what conditions is it unreliable?

The kernel checks IRQF_DISABLED bit of only the first handler
even if multiple handlers are assigned to a single IRQ line.
Thus, if another handler without IRQF_DISABLED has been already
registered before yours, your IRQF_DISABLED is ignored.

See kernel/irq/handle.c.


Takashi
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