Messages in this thread | | | Date | Thu, 7 Nov 2019 11:22:01 +0000 | From | Will Deacon <> | Subject | Re: [PATCH 1/5] smp_mb__{before,after}_atomic(): Update Documentation |
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Hi Manfred,
On Wed, Nov 06, 2019 at 08:23:03PM +0100, Manfred Spraul wrote: > 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();
Thanks, I much prefer this approach:
Acked-by: Will Deacon <will@kernel.org>
Will
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