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author | Manfred Spraul <manfred@colorfullife.com> | 2020-02-03 17:34:29 -0800 |
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committer | Linus Torvalds <torvalds@linux-foundation.org> | 2020-02-04 03:05:23 +0000 |
commit | 39323c64b8a95d10ddc66dc815dd14efdddf6777 (patch) | |
tree | 2221c4326ef7fa9ff3f4e773f51c38246c6f64ca | |
parent | 92917998849eea951707c8fea2dc3007bb2ad2cd (diff) | |
download | linux-39323c64b8a95d10ddc66dc815dd14efdddf6777.tar.gz linux-39323c64b8a95d10ddc66dc815dd14efdddf6777.tar.bz2 linux-39323c64b8a95d10ddc66dc815dd14efdddf6777.zip |
smp_mb__{before,after}_atomic(): update Documentation
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.
Link: http://lkml.kernel.org/r/20191020123305.14715-2-manfred@colorfullife.com
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>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: <1vier1@web.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r-- | Documentation/memory-barriers.txt | 16 |
1 files changed, 10 insertions, 6 deletions
diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt index ec3b5865c1be..7146da061693 100644 --- a/Documentation/memory-barriers.txt +++ b/Documentation/memory-barriers.txt @@ -1868,12 +1868,16 @@ 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: |