Jamie Lokier wrote:
> Look in arch/arm/kernel/entry-armv.S for __kernel_cmpxchg,
> kuser_cmpxchg_fixup, and all the places where kuser_cmpxchg_fixup is
> called in that file.
>
Here they say:
/*
* The only thing that can break atomicity in this cmpxchg
* implementation is either an IRQ or a data abort exception
* causing another process/thread to be scheduled in the middle
* of the critical sequence. To prevent this, code is added to
* the IRQ and data abort exception handlers to set the pc back
* to the beginning of the critical section if it is found to be
* within that critical section (see kuser_cmpxchg_fixup).
*/
So the "trick" involves modifying the basic interrupt handler code.
This of course is a *nasty* trick.
I'll take a look if this is viable for the NIOS architecture.
Thanks for pointing me there,
-Michael
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