Missing memory fences in mutexes

[socketpair]

https://en.m.wikipedia.org/wiki/Memory_barrier#Multithreaded_programming_and_memory_visibility

You need mfence/lfence/sfence before mutex_lock() returns, and before unlock() returns.

[socketpair]

Thread 1:
Lock
A=1
Unlock

Thread 2:
Lock
Read A. May see old, not updated by thread 1 value.

[nemasu]

Thanks for this! Sorry for the incredibly late response. The mutex isn't being used at the moment, but I'll try to add these system calls anyways though just so it's usable if it's ever needed.