Messages in this thread Patch in this message | | | Subject | Re: [PATCH 1/5] smp_mb__{before,after}_atomic(): Update Documentation | From | Manfred Spraul <> | Date | Wed, 6 Nov 2019 20:23:03 +0100 |
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Hi Will,
On 11/1/19 5:49 PM, Will Deacon wrote: > 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. > [...] > > 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 It's just duplication and is out of date.
So you would prefer the attached patch?
For me this would be fine, too.
--
Manfred
From 8d2b219794221e3ef1a1ec90e0f4fe344af9a55d Mon Sep 17 00:00:00 2001 From: Manfred Spraul <manfred@colorfullife.com> Date: Fri, 11 Oct 2019 10:33:26 +0200 Subject: [PATCH 1/5] 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_atomic and smp_mb__after_atomic can be combined with all RMW operations that do not imply memory barriers.
In order to avoid that this happens again: Remove the paragraph from Documentation/memory_barrier.txt, the functions are sufficiently documented in Documentation/atomic_{t,bitops}.txt
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 | 20 +------------------- 1 file changed, 1 insertion(+), 19 deletions(-)
diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt index 1adbb8a371c7..16dfb4cde1e1 100644 --- a/Documentation/memory-barriers.txt +++ b/Documentation/memory-barriers.txt @@ -1873,25 +1873,7 @@ 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). - - As an example, consider a piece of code that marks an object as being dead - and then decrements the object's reference count: - - obj->dead = 1; - smp_mb__before_atomic(); - atomic_dec(&obj->ref_count); - - This makes sure that the death mark on the object is perceived to be set - *before* the reference counter is decremented. - - See Documentation/atomic_{t,bitops}.txt for more information. - + See Documentation/atomic_{t,bitops}.txt for information. (*) dma_wmb(); (*) dma_rmb(); -- 2.23.0
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