linux-kernel - [PATCH 3.12 62/82] rcu: Move lockless

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Date:	Mon, 24 Aug 2015 11:09:22 +0200
From:	Jiri Slaby <jslaby@...e.cz>
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Paul McKenney <paulmck@...ux.vnet.ibm.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 62/82] rcu: Move lockless_dereference() out of rcupdate.h

From: Peter Zijlstra <peterz@...radead.org>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

commit 0a04b0166929405cd833c1cc40f99e862b965ddc upstream.

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@...ux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 include/linux/compiler.h | 15 +++++++++++++++
 include/linux/rcupdate.h | 15 ---------------
 2 files changed, 15 insertions(+), 15 deletions(-)

diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 2472740d7ab2..4a3caa61a002 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -364,6 +364,21 @@ void ftrace_likely_update(struct ftrace_branch_data *f, int val, int expect);
  */
 #define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(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 4912c953cab7..965725f957d9 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -555,21 +555,6 @@ static inline void rcu_preempt_sleep_check(void)
 	} 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
  * @p: The pointer to read
  *
-- 
2.5.0

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