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authorPeter Zijlstra <peterz@infradead.org>2015-05-27 04:39:36 +0300
committerRusty Russell <rusty@rustcorp.com.au>2015-05-28 05:02:05 +0300
commit0a04b0166929405cd833c1cc40f99e862b965ddc (patch)
treec108e2aee50ce533cef248c755e86d48c59a4ebf /include/linux/compiler.h
parent6695b92a60bc7160c92d6dc5b17cc79673017c2f (diff)
downloadlinux-0a04b0166929405cd833c1cc40f99e862b965ddc.tar.xz
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>
Diffstat (limited to 'include/linux/compiler.h')
-rw-r--r--include/linux/compiler.h15
1 files changed, 15 insertions, 0 deletions
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index 867722591be2..eae42c21d5fd 100644
--- 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")))