Messages in this thread | | | Date | Fri, 1 Nov 2019 16:49:48 +0000 | From | Will Deacon <> | Subject | Re: [PATCH 1/5] smp_mb__{before,after}_atomic(): Update Documentation |
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Hi Manfred,
On Sun, Oct 20, 2019 at 02:33:01PM +0200, Manfred Spraul wrote: > 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.
[...]
> 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,
typo: "are memory barrier"
> + 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).
Although I think this is correct, I really think we should instead refer to Documentation/atomic_t.txt and get rid of this out of memory-barriers.txt entirely. It's just duplication and is out of date.
Will
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