From: "Paul E. McKenney" <[email protected]> 3.12-stable review patch. If anyone has any objections, please let me know.
=============== commit 54ef6df3f3f1353d99c80c437259d317b2cd1cbd upstream. 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 <[email protected]> Signed-off-by: Paul E. McKenney <[email protected]> Signed-off-by: Al Viro <[email protected]> Signed-off-by: Jiri Slaby <[email protected]> --- include/linux/rcupdate.h | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index f1f1bc39346b..4912c953cab7 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -554,6 +554,20 @@ static inline void rcu_preempt_sleep_check(void) (p) = (typeof(*v) __force space *)(v); \ } while (0) +/** + * 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_access_pointer() - fetch RCU pointer with no dereferencing -- 2.5.0 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
