Greg Kroah-Hartman
598cf27219
Link: https://lore.kernel.org/r/20260217200002.683975158@linuxfoundation.org Tested-by: Florian Fainelli <florian.fainelli@broadcom.com> Tested-by: Takeshi Ogasawara <takeshi.ogasawara@futuring-girl.com> Tested-by: Peter Schneider <pschneider1968@googlemail.com> Tested-by: Jon Hunter <jonathanh@nvidia.com> Tested-by: Salvatore Bonaccorso <carnil@debian.org> Tested-by: Brett A C Sheffield <bacs@librecast.net> Tested-by: Mark Brown <broonie@kernel.org> Tested-by: Luna Jernberg <droidbittin@gmail.com> Tested-by: Ronald Warsow <rwarsow@gmx.de> Tested-by: Justin M. Forbes <jforbes@fedoraproject.org> Tested-by: Ron Economos <re@w6rz.net> Tested-by: Miguel Ojeda <ojeda@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
70 lines
1.4 KiB
Plaintext
70 lines
1.4 KiB
Plaintext
=============
|
|
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.
|
|
|
|
|
|
API
|
|
---
|
|
|
|
The single bit operations are:
|
|
|
|
Non-RMW ops:
|
|
|
|
test_bit()
|
|
|
|
RMW atomic operations without return value:
|
|
|
|
{set,clear,change}_bit()
|
|
clear_bit_unlock()
|
|
|
|
RMW atomic operations with return value:
|
|
|
|
test_and_{set,clear,change}_bit()
|
|
test_and_set_bit_lock()
|
|
|
|
Barriers:
|
|
|
|
smp_mb__{before,after}_atomic()
|
|
|
|
|
|
All RMW atomic operations have a '__' prefixed variant which is non-atomic.
|
|
|
|
|
|
SEMANTICS
|
|
---------
|
|
|
|
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.
|
|
|
|
|
|
ORDERING
|
|
--------
|
|
|
|
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 fully ordered.
|
|
|
|
Except for a successful test_and_set_bit_lock() which has ACQUIRE semantics,
|
|
clear_bit_unlock() which has RELEASE semantics and test_bit_acquire which has
|
|
ACQUIRE 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.
|
|
|