LDREX/STREX and pre-emption on SMP hardware

Catalin Marinas wrote:

On Fri, 2009-08-21 at 16:07 +0100, Richard Crewe wrote:

quoted

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