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Date: Sun, 13 Jan 2002 19:06:33 +0000
From: Russell King <rmk@arm.linux.org.uk>
To: Robert Love <rml@tech9.net>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>, arjan@fenrus.demon.nl,
        Rob Landley <landley@trommello.org>, linux-kernel@vger.kernel.org
Subject: Re: [2.4.17/18pre] VM and swap - it's really unusable
Message-ID: <20020113190633.B14469@flint.arm.linux.org.uk>
In-Reply-To: <E16PUeP-00034K-00@the-village.bc.nu> <1010891457.3561.18.camel@phantasy> <20020113113941.B13566@flint.arm.linux.org.uk> <1010946261.11852.16.camel@phantasy>
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In-Reply-To: <1010946261.11852.16.camel@phantasy>; from rml@tech9.net on Sun, Jan 13, 2002 at 01:24:20PM -0500
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On Sun, Jan 13, 2002 at 01:24:20PM -0500, Robert Love wrote:
> On Sun, 2002-01-13 at 06:39, Russell King wrote:
> > On Sat, Jan 12, 2002 at 10:10:55PM -0500, Robert Love wrote:
> > > It can if we increment the preempt_count in disable_irq_nosync and
> > > decrement it on enable_irq.
> > 
> > Who says you're going to be enabling IRQs any time soon?  AFAIK, there is
> > nothing that requires enable_irq to be called after disable_irq_nosync.
> > 
> > In fact, you could well have the following in a driver:
> > 
> > 	/* initial shutdown of device */
> > 
> > 	disable_irq_nosync(i); /* or disable_irq(i); */
> > 
> > 	/* other shutdown stuff */
> > 
> > 	free_irq(i, private);
> > 
> > and you would have to audit all drivers to find out if they did this -
> > this would seriously damage your preempt_count.
> 
> I wasn't thinking.  Anytime we are in an interrupt handler, preemption
> is disabled.  Regardless of how (or even if) interrupts are disabled. 
> We bump preempt_count on the entry path.  So, no problem.

Err.  This isn't *inside* an interrupt handler.  This could well be in
the driver shutdown code (eg, when fops->release is called).

-- 
Russell King (rmk@arm.linux.org.uk)                The developer of ARM Linux
             http://www.arm.linux.org.uk/personal/aboutme.html

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