path: root/Documentation
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authorWill Deacon <>2017-10-24 11:22:49 +0100
committerIngo Molnar <>2017-10-24 13:17:33 +0200
commit59ecbbe7b31cd2d86ff9a9f461a00f7e7533aedc (patch)
treecb293c6c7810f9d781bb6f0c4017b2b3dd8a27bb /Documentation
parent506458efaf153c1ea480591c5602a5a3ba5a3b76 (diff)
locking/barriers: Kill lockless_dereference()
lockless_dereference() is a nice idea, but it gained little traction in kernel code since its introduction three years ago. This is partly because it's a pain to type, but also because using READ_ONCE() instead has worked correctly on all architectures apart from Alpha, which is a fully supported but somewhat niche architecture these days. Now that READ_ONCE() has been upgraded to contain an implicit smp_read_barrier_depends() and the few callers of lockless_dereference() have been converted, we can remove lockless_dereference() altogether. Signed-off-by: Will Deacon <> Cc: Linus Torvalds <> Cc: Paul E. McKenney <> Cc: Peter Zijlstra <> Cc: Thomas Gleixner <> Link: Signed-off-by: Ingo Molnar <>
Diffstat (limited to 'Documentation')
2 files changed, 0 insertions, 24 deletions
diff --git a/Documentation/memory-barriers.txt b/Documentation/memory-barriers.txt
index b759a60624fd..470a682f3fa4 100644
--- a/Documentation/memory-barriers.txt
+++ b/Documentation/memory-barriers.txt
@@ -1886,18 +1886,6 @@ There are some more advanced barrier functions:
See Documentation/atomic_{t,bitops}.txt for more information.
- (*) lockless_dereference();
- This can be thought of as a pointer-fetch wrapper around the
- smp_read_barrier_depends() data-dependency barrier.
- This is also similar to rcu_dereference(), but in cases where
- object lifetime is handled by some mechanism other than RCU, for
- example, when the objects removed only when the system goes down.
- In addition, lockless_dereference() is used in some data structures
- that can be used both with and without RCU.
(*) dma_wmb();
(*) dma_rmb();
diff --git a/Documentation/translations/ko_KR/memory-barriers.txt b/Documentation/translations/ko_KR/memory-barriers.txt
index a7a813258013..ec3b46e27b7a 100644
--- a/Documentation/translations/ko_KR/memory-barriers.txt
+++ b/Documentation/translations/ko_KR/memory-barriers.txt
@@ -1858,18 +1858,6 @@ Mandatory 배리어들은 SMP 시스템에서도 UP 시스템에서도 SMP 효
- (*) lockless_dereference();
- 이 함수는 smp_read_barrier_depends() 데이터 의존성 배리어를 사용하는
- 포인터 읽어오기 래퍼(wrapper) 함수로 생각될 수 있습니다.
- 객체의 라이프타임이 RCU 외의 메커니즘으로 관리된다는 점을 제외하면
- rcu_dereference() 와도 유사한데, 예를 들면 객체가 시스템이 꺼질 때에만
- 제거되는 경우 등입니다. 또한, lockless_dereference() 은 RCU 와 함께
- 사용될수도, RCU 없이 사용될 수도 있는 일부 데이터 구조에 사용되고
- 있습니다.
(*) dma_wmb();
(*) dma_rmb();