Re: spin-locks

[Richard B. Johnson]

On Fri, 10 May 2002, David Woodhouse wrote:

> 
> [e-mail] said:
> >  Well, here is code that worked on linux 2.2.17.  Same CPUs, same
> > everything... Just a different version of OS...
> 
> I suspect your code was protected by the BKL in 2.2.17, not by your 
> 'spinlocks'.
> 
> [e-mail] said:
> > 	cli
> > 	lock
> > 	incb	(lockf)		# Bump lock-value 
> 
> Ponder what happens if two CPUs get here at the same time. Lock count is 
> now two.
> 
> > 1:	cmpb	$1,(lockf)	# See if we own it
> > 	jnz	1b		# Nope, spin until we do. 
> 
> Now they both spin forever.

Yep. You are correct. Obvious bug that went undetected for over
a year.

Cheers,
Dick Johnson

Penguin : Linux version 2.4.18 on an i686 machine (797.90 BogoMips).

                 Windows-2000/Professional isn't.