LDREX/STREX and pre-emption on SMP hardware

[Jamie Lokier]

Catalin Marinas wrote:
> On Fri, 2009-08-21 at 16:07 +0100, Richard Crewe wrote:
> > Section A2.9.3 of the ARM architecture ref. manual seems to imply that 
> > ldrex/strex instruction pairs won't work correctly if they are nested 
> > due to pre-emption.
> > 
> > Should a strex instruction be added to the low-level interrupt handler 
> > or should all ldrex/strex instruction pairs be protected from 
> > pre-emption by disabling interrupts?
> 
> There is no need to since preemption means rescheduling which implies a
> call to the __switch_to function in entry-armv.S. This function clears
> the exclusive monitor state explicitly.

What about when an interrupt handler uses ldrex/strex?  There is no
call to __switch_to.

-- Jamie