rcu: Move lockless_dereference() out of rcupdate.h

I want to use lockless_dereference() from seqlock.h, which would mean
including rcupdate.h from it, however rcupdate.h already includes
seqlock.h.

Avoid this by moving lockless_dereference() into compiler.h. This is
somewhat tricky since it uses smp_read_barrier_depends() which isn't
available there, but its a CPP macro so we can get away with it.

The alternative would be moving it into asm/barrier.h, but that would
be updating each arch (I can do if people feel that is more
appropriate).

Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 867722591be2c7e026e1b97c241e65e27e3b9d1b..eae42c21d5fde9816b3cae961b19dda05e29158a 100644 (file)
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -457,6 +457,21 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s
        (volatile typeof(x) *)&(x); })
 #define ACCESS_ONCE(x) (*__ACCESS_ONCE(x))
 
+/**
+ * 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); \
+})
+
 /* Ignore/forbid kprobes attach on very low level functions marked by this attribute: */
 #ifdef CONFIG_KPROBES
 # define __kprobes     __attribute__((__section__(".kprobes.text")))

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 573a5afd5ed884d5bdcfc4af6cf88c3b9d25214d..0356ad954ea568cb4e5b03a4d5a6b13c83c28386 100644 (file)
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -649,21 +649,6 @@ 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