[RFC] atomic_up operations

Hi,

LTTng 0.6.28-29 introduces asm-*/atomic-up.h which has atomic operations without
LOCK prefix event on SMP. This is for atomic access of per-cpu data.

RFC : cmpxchg is implemented in asm-*/system.h. I always thought it was a weird
design choice. I would much prefer to put it in asm-*/atomic.h, thus placing my
cmpxchg_up in atomic-up.h. Otherwise, I have to modify system.h, which is what I
currently do and would like to avoid.

Mathieu

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