xv6-cs450/spinlock.h

// Mutual exclusion lock.
struct spinlock {
  uint locked;   // Is the lock held?
  
  // For debugging:
  char *name;    // Name of lock.
  int  cpu;      // The number of the cpu holding the lock.
  uint pcs[10];  // The call stack (an array of program counters)
                 // that locked the lock.
};