LDREX/STREX and pre-emption on SMP hardware

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?

I have a suspicion that this may only cause problems on SMP systems.

-- 
Rich