riot-rs-threads: cortex-m: add compiler fence around wfi
dance
#312
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Fixes Cortex-M
sched()
not seeing changes to the runqueue.See #310 (comment).
As to why the fence is necessary, I cannot explain. The critical section should actually imply a fence. In this case, the runqueue accesses are heavily inlined, so maybe something is off with the optimizer. Or, we're doing something wrong with how we access
THREADS
, which is a lot more likely than a compiler bug. 😏