Commit 49070961 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Luis Henriques

rcu: Move lockless_dereference() out of rcupdate.h

commit 0a04b016 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@linux.vnet.ibm.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: default avatarRusty Russell <rusty@rustcorp.com.au>
[ luis: 3.16 prereq for:
  37868fe1 "x86/ldt: Make modify_ldt synchronous" ]
Signed-off-by: default avatarLuis Henriques <luis.henriques@canonical.com>
parent 4903dc9f
...@@ -380,6 +380,21 @@ void ftrace_likely_update(struct ftrace_branch_data *f, int val, int expect); ...@@ -380,6 +380,21 @@ void ftrace_likely_update(struct ftrace_branch_data *f, int val, int expect);
*/ */
#define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(x)) #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: */ /* Ignore/forbid kprobes attach on very low level functions marked by this attribute: */
#ifdef CONFIG_KPROBES #ifdef CONFIG_KPROBES
# define __kprobes __attribute__((__section__(".kprobes.text"))) # define __kprobes __attribute__((__section__(".kprobes.text")))
......
...@@ -592,21 +592,6 @@ static inline void rcu_preempt_sleep_check(void) ...@@ -592,21 +592,6 @@ static inline void rcu_preempt_sleep_check(void)
*/ */
#define RCU_INITIALIZER(v) (typeof(*(v)) __force __rcu *)(v) #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 * rcu_assign_pointer() - assign to RCU-protected pointer
* @p: pointer to assign to * @p: pointer to assign to
......
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