What happens when you sleep

Once again a joy ride of a roller coaster that is the Linux kernel.

What happens when you sleep in the kernel. You here is the process context code that has either voluntarily relinquished the CPU or because it was doing a blocking call.

/**
   * mutex_lock - acquire the mutex
   * @lock: the mutex to be acquired
   *
   * Lock the mutex exclusively for this task. If the mutex is not
   * available right now, it will sleep until it can get it.
   *
   * The mutex must later on be released by the same task that
   * acquired it. Recursive locking is not allowed. The task
   * may not exit without first unlocking the mutex. Also, kernel
   * memory where the mutex resides must not be freed with
   * the mutex still locked. The mutex must first be initialized
   * (or statically defined) before it can be locked. memset()-ing
   * the mutex to 0 is not allowed.
   *
   * ( The CONFIG_DEBUG_MUTEXES .config option turns on debugging
   *   checks that will enforce the restrictions and will also do
   *   deadlock debugging. )
   *
   * This function is similar to (but not equivalent to) down().
   */
  void __sched mutex_lock(struct mutex *lock)
  {
        might_sleep();  //---> Just for Debugging.
        /*
         * The locking fastpath is the 1->0 transition from
        * 'unlocked' into 'locked' state.
        */
      __mutex_fastpath_lock(&lock->count, __mutex_lock_slowpath);
       mutex_set_owner(lock);
 }
 
 EXPORT_SYMBOL(mutex_lock);

Ingo Molnar's function header sums it up.