From 0a04b0166929405cd833c1cc40f99e862b965ddc Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Wed, 27 May 2015 11:09:36 +0930 Subject: 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 Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Rusty Russell --- include/linux/compiler.h | 15 +++++++++++++++ 1 file changed, 15 insertions(+) (limited to 'include/linux/compiler.h') 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"))) -- cgit v1.2.1 From 38183b9c31cf21d8996d6eee2e3a14508b20c418 Mon Sep 17 00:00:00 2001 From: Stephen Rothwell Date: Thu, 28 May 2015 17:20:58 +1000 Subject: rcu: merge fix for Convert ACCESS_ONCE() to READ_ONCE() and WRITE_ONCE() This mirrors the change introduced by 7d0ae8086b8 of same title in Linus' tree; it's not obvious as a merge resolution since we moved the function. Signed-off-by: Stephen Rothwell Signed-off-by: Rusty Russell --- include/linux/compiler.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'include/linux/compiler.h') diff --git a/include/linux/compiler.h b/include/linux/compiler.h index eae42c21d5fd..52bdec710ed7 100644 --- a/include/linux/compiler.h +++ b/include/linux/compiler.h @@ -467,7 +467,7 @@ static __always_inline void __write_once_size(volatile void *p, void *res, int s */ #define lockless_dereference(p) \ ({ \ - typeof(p) _________p1 = ACCESS_ONCE(p); \ + typeof(p) _________p1 = READ_ONCE(p); \ smp_read_barrier_depends(); /* Dependency order vs. p above. */ \ (_________p1); \ }) -- cgit v1.2.1