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WAKE_UP_BIT(9) Driver Basics WAKE_UP_BIT(9)


wake_up_bit - wake up a waiter on a bit


void wake_up_bit(void * word, int bit);



the word being waited on, a kernel virtual address


the bit of the word being waited on


There is a standard hashed waitqueue table for generic use. This is the part of the hashtable's 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_atomic, 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.c's smp_mb, because spin_unlock does not guarantee a memory barrier.


January 2017 Kernel Hackers Manual 4.8.