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 <will.deacon@arm.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1508840570-22169-5-git-send-email-will.deacon@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 0 insertions, 12 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();