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Commit 0a04b016 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Rusty Russell
Browse files

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: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatarRusty Russell <rusty@rustcorp.com.au>
parent 6695b92a

include/linux/compiler.h

+15 −0
Original line number Diff line number Diff line
@@ -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")))

include/linux/rcupdate.h

+0 −15
Original line number Diff line number Diff line
@@ -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