Mastering Linux Kernel Development

Waiting for completion

If any thread needs to wait for a task to complete, it will call wait_for_completion() on the initialized completion structure. If the wait_for_completion operation happens after the call to complete() or complete_all(), the thread simply continues, as the reason it wanted to wait for has been satisfied; else, it waits till complete() is signalled. There are variants available for the wait_for_completion() calls:

extern void wait_for_completion_io(struct completion *);
extern int wait_for_completion_interruptible(struct completion *x);
extern int wait_for_completion_killable(struct completion *x);
extern unsigned long wait_for_completion_timeout(struct completion *x,
                                                   unsigned long timeout);
extern unsigned long wait_for_completion_io_timeout ...