Re: Possible race condition in i386 global_irq_lock handling.

[Andrea Arcangeli <andrea@suse.de>]

On Thu, Aug 21, 2003 at 11:48:24PM +0200, Stephan von Krawczynski wrote:
> 
> > smb_rmb is enough in practice for x86 (in asm-i386), but not the right
> > barrier in general because rmb only serializes reads against reads, so
> > it would also make little sense while reading the i386 code. here you've
> > to serialize a write against a read so it would be misleading unless you
> > know exactly the lowlevel implementations of those barriers.
> > 
> > smp_mb() before the while loop should be the correct barrier for all
> > archs and the asm generated on x86 will be the same.
> > 
> > alpha, ia64 and x86-64 (and probably others) needs it too.
> 
> Can some kind soul please provide me with the needed mini-patch. I would like
> to try that on my constantly crashing SMP test box...

--- 2.4.22pre7aa1/include/asm-i386/hardirq.h.~1~	2003-07-20 18:39:04.000000000 +0200
+++ 2.4.22pre7aa1/include/asm-i386/hardirq.h	2003-08-22 00:24:08.000000000 +0200
@@ -71,6 +71,8 @@ static inline void irq_enter(int cpu, in
 {
 	++local_irq_count(cpu);
 
+	smp_mb();
+
 	while (test_bit(0,&global_irq_lock)) {
 		cpu_relax();
 	}

Andrea