blob: 093cdaefdb3733ecd076b5ffbfe3ad880b2c3afd [file] [log] [blame]
Atomic bitops
While our bitmap_{}() functions are non-atomic, we have a number of operations
operating on single bits in a bitmap that are atomic.
The single bit operations are:
Non-RMW ops:
RMW atomic operations without return value:
RMW atomic operations with return value:
All RMW atomic operations have a '__' prefixed variant which is non-atomic.
Non-atomic ops:
In particular __clear_bit_unlock() suffers the same issue as atomic_set(),
which is why the generic version maps to clear_bit_unlock(), see atomic_t.txt.
RMW ops:
The test_and_{}_bit() operations return the original value of the bit.
Like with atomic_t, the rule of thumb is:
- non-RMW operations are unordered;
- RMW operations that have no return value are unordered;
- RMW operations that have a return value are fully ordered.
- RMW operations that are conditional are unordered on FAILURE,
otherwise the above rules apply. In the case of test_and_{}_bit() operations,
if the bit in memory is unchanged by the operation then it is deemed to have
Except for a successful test_and_set_bit_lock() which has ACQUIRE semantics and
clear_bit_unlock() which has RELEASE semantics.
Since a platform only has a single means of achieving atomic operations
the same barriers as for atomic_t are used, see atomic_t.txt.