returns non zero. If v is equal to u then it returns zero. This is done as
an atomic operation.
-atomic_add_unless requires explicit memory barriers around the operation.
+atomic_add_unless requires explicit memory barriers around the operation
+unless it fails (returns 0).
atomic_inc_not_zero, equivalent to atomic_add_unless(v, 1, 0)
*/
smp_mb__after_clear_bit();
+There are two special bitops with lock barrier semantics (acquire/release,
+same as spinlocks). These operate in the same way as their non-_lock/unlock
+postfixed variants, except that they are to provide acquire/release semantics,
+respectively. This means they can be used for bit_spin_trylock and
+bit_spin_unlock type operations without specifying any more barriers.
+
+ int test_and_set_bit_lock(unsigned long nr, unsigned long *addr);
+ void clear_bit_unlock(unsigned long nr, unsigned long *addr);
+ void __clear_bit_unlock(unsigned long nr, unsigned long *addr);
+
+The __clear_bit_unlock version is non-atomic, however it still implements
+unlock barrier semantics. This can be useful if the lock itself is protecting
+the other bits in the word.
+
Finally, there are non-atomic versions of the bitmask operations
provided. They are used in contexts where some other higher-level SMP
locking scheme is being used to protect the bitmask, and thus less