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//0x20 bytes (sizeof)
struct _FAST_MUTEX
{
    volatile LONG Count;                                                    //0x0
    struct _KTHREAD* Owner;                                                 //0x4
    ULONG Contention;                                                       //0x8
    struct _KEVENT Event;                                                   //0xc
    ULONG OldIrql;                                                          //0x1c
};