+ smp_mb__beforeafter_atomic-update-documentation.patch added to -mm tree

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The patch titled
     Subject: smp_mb__{before,after}_atomic(): update Documentation
has been added to the -mm tree.  Its filename is
     smp_mb__beforeafter_atomic-update-documentation.patch

This patch should soon appear at
    http://ozlabs.org/~akpm/mmots/broken-out/smp_mb__beforeafter_atomic-update-documentation.patch
and later at
    http://ozlabs.org/~akpm/mmotm/broken-out/smp_mb__beforeafter_atomic-update-documentation.patch

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------------------------------------------------------
From: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>
Subject: 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@xxxxxxxxxxxxxxxx
Fixes: 654672d4ba1a ("locking/atomics: Add _{acquire|release|relaxed}() variants of some atomic operations")
Signed-off-by: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>
Acked-by: Waiman Long <longman@xxxxxxxxxx>
Cc: Davidlohr Bueso <dave@xxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: <1vier1@xxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 Documentation/memory-barriers.txt |   14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

--- a/Documentation/memory-barriers.txt~smp_mb__beforeafter_atomic-update-documentation
+++ a/Documentation/memory-barriers.txt
@@ -1873,12 +1873,16 @@ There are some more advanced barrier fun
  (*) 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 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 bitop functions that do not return a
-     value (such as set_bit and clear_bit).
+     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:
_

Patches currently in -mm which might be from manfred@xxxxxxxxxxxxxxxx are

smp_mb__beforeafter_atomic-update-documentation.patch
ipc-mqueuec-update-document-memory-barriers.patch
ipc-msgc-update-and-document-memory-barriers.patch
ipc-semc-document-and-update-memory-barriers.patch




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