mirror of
https://github.com/torvalds/linux.git
synced 2024-11-23 20:51:44 +00:00
4961836468
This document misses a title. Add it, in order to follow the documentation standard. Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
72 lines
1.5 KiB
Plaintext
72 lines
1.5 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 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
|
|
failed.
|
|
|
|
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.
|
|
|