Messages in this thread Patch in this message | | | From | Manfred Spraul <> | Subject | [PATCH 1/5] smp_mb__{before,after}_atomic(): Update Documentation | Date | Sun, 20 Oct 2019 14:33:01 +0200 |
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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 <manfred@colorfullife.com> Acked-by: Waiman Long <longman@redhat.com> Cc: Davidlohr Bueso <dave@stgolabs.net> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Will Deacon <will.deacon@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
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