From: Manfred Spraul <manfred@colorfullife.com>
To: LKML <linux-kernel@vger.kernel.org>,
Davidlohr Bueso <dave@stgolabs.net>,
Waiman Long <longman@redhat.com>
Cc: 1vier1@web.de, Andrew Morton <akpm@linux-foundation.org>,
Peter Zijlstra <peterz@infradead.org>,
Manfred Spraul <manfred@colorfullife.com>,
Will Deacon <will.deacon@arm.com>
Subject: [PATCH 1/5] smp_mb__{before,after}_atomic(): Update Documentation
Date: Sun, 20 Oct 2019 14:33:01 +0200 [thread overview]
Message-ID: <20191020123305.14715-2-manfred@colorfullife.com> (raw)
In-Reply-To: <20191020123305.14715-1-manfred@colorfullife.com>
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.
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 | 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,
+ 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:
--
2.21.0
next prev parent reply other threads:[~2019-10-20 12:33 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-20 12:33 [PATCH 0/5] V3: Clarify/standardize memory barriers for ipc Manfred Spraul
2019-10-20 12:33 ` Manfred Spraul [this message]
2019-11-01 16:49 ` [PATCH 1/5] smp_mb__{before,after}_atomic(): Update Documentation Will Deacon
2019-11-06 19:23 ` Manfred Spraul
2019-11-07 11:22 ` Will Deacon
2019-10-20 12:33 ` [PATCH 2/5] ipc/mqueue.c: Remove duplicated code Manfred Spraul
2019-10-22 22:43 ` Andrew Morton
2019-10-20 12:33 ` [PATCH 3/5] ipc/mqueue.c: Update/document memory barriers Manfred Spraul
2019-10-20 12:33 ` [PATCH 4/5] ipc/msg.c: Update and document " Manfred Spraul
2019-10-20 12:33 ` [PATCH 5/5] ipc/sem.c: Document and update " Manfred Spraul
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