Re: [2.4.17/18pre] VM and swap - it's really unusable

[Russell King]

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 ([e-mail])                The developer of ARM Linux
             http://www.arm.linux.org.uk/personal/aboutme.html