When adding the _{acquire|release|relaxed}() variants of some atomic
operations, it was forgotten to update Documentation/memory_barrier.txt:
smp_mb__{before,after}_atomic() is now intended for all RMW operations
that do not imply a memory barrier.
1)
smp_mb__before_atomic();
atomic_add();
2)
smp_mb__before_atomic();
atomic_xchg_relaxed();
3)
smp_mb__before_atomic();
atomic_fetch_add_relaxed();
Invalid would be:
smp_mb__before_atomic();
atomic_set();
In addition, the patch splits the long sentence into multiple shorter
sentences.
Fixes: 654672d4ba1a ("locking/atomics: Add _{acquire|release|relaxed}()
variants of some atomic operations")
Signed-off-by: Manfred Spraul <manf...@colorfullife.com>
Acked-by: Waiman Long <long...@redhat.com>
Cc: Davidlohr Bueso <d...@stgolabs.net>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Will Deacon <will.dea...@arm.com>
---
Documentation/memory-barriers.txt | 16 ++++++++++------
1 file changed, 10 insertions(+), 6 deletions(-)
diff --git a/Documentation/memory-barriers.txt
b/Documentation/memory-barriers.txt
index 1adbb8a371c7..fe43f4b30907 100644
--- a/Documentation/memory-barriers.txt
+++ b/Documentation/memory-barriers.txt
@@ -1873,12 +1873,16 @@ There are some more advanced barrier functions:
(*) smp_mb__before_atomic();
(*) smp_mb__after_atomic();
- These are for use with atomic (such as add, subtract, increment and
- decrement) functions that don't return a value, especially when used for
- reference counting. These functions do not imply memory barriers.
-
- These are also used for atomic bitop functions that do not return a
- value (such as set_bit and clear_bit).
+ These are for use with atomic RMW functions that do not imply memory
+ barriers, but where the code needs a memory barrier. Examples for atomic
+ RMW functions that do not imply are memory barrier are e.g. add,
+ subtract, (failed) conditional operations, _relaxed functions,
+ but not atomic_read or atomic_set. A common example where a memory
+ barrier may be required is when atomic ops are used for reference
+ counting.
+
+ These are also used for atomic RMW bitop functions that do not imply a
+ memory barrier (such as set_bit and clear_bit).
As an example, consider a piece of code that marks an object as being dead
and then decrements the object's reference count:
--
2.21.0
