From 54ef6df3f3f1353d99c80c437259d317b2cd1cbd Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 27 Oct 2014 21:11:27 -0700 Subject: [PATCH 1/1] rcu: Provide counterpart to rcu_dereference() for non-RCU situations Although rcu_dereference() and friends can be used in situations where object lifetimes are being managed by something other than RCU, the resulting sparse and lockdep-RCU noise can be annoying. This commit therefore supplies a lockless_dereference(), which provides the protection for dereferences without the RCU-related debugging noise. Reported-by: Al Viro Signed-off-by: Paul E. McKenney Signed-off-by: Al Viro --- include/linux/rcupdate.h | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index a4a819ffb2d1..53ff1a752d7e 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -616,6 +616,21 @@ static inline void rcu_preempt_sleep_check(void) */ #define RCU_INITIALIZER(v) (typeof(*(v)) __force __rcu *)(v) +/** + * lockless_dereference() - safely load a pointer for later dereference + * @p: The pointer to load + * + * Similar to rcu_dereference(), but for situations where the pointed-to + * object's lifetime is managed by something other than RCU. That + * "something other" might be reference counting or simple immortality. + */ +#define lockless_dereference(p) \ +({ \ + typeof(p) _________p1 = ACCESS_ONCE(p); \ + smp_read_barrier_depends(); /* Dependency order vs. p above. */ \ + (_________p1); \ +}) + /** * rcu_assign_pointer() - assign to RCU-protected pointer * @p: pointer to assign to -- 2.20.1