Man page 9 : wake_up_bit

wake_up_bit - wake up a waiter on a bit

void wake_up_bit(void *  word , int  bit );

word
    the word being waited on, a kernel virtual address

bit
    the bit of the word being waited on

There is a standard hashed waitqueue table for generic use. This is the part of the hashtableAqs accessor API that wakes up waiters on a bit. For instance, if one were to have waiters on a bitflag, one would call wake_up_bit after clearing the bit.

In order for this to function properly, as it uses waitqueue_active internally, some kind of memory barrier must be done prior to calling this. Typically, this will be smp_mb__after_clear_bit, but in some cases where bitflags are manipulated non-atomically under a lock, one may need to use a less regular barrier, such fs/inode.cAqs smp_mb, because spin_unlock does not guarantee a memory barrier.