Commit 4903dc9f authored by Paul E. McKenney's avatar Paul E. McKenney Committed by Luis Henriques

rcu: Provide counterpart to rcu_dereference() for non-RCU situations

commit 54ef6df3 upstream.

Although rcu_dereference() and friends can be used in situations where
object lifetimes are being managed by something other than RCU, the
resulting sparse and lockdep-RCU noise can be annoying.  This commit
therefore supplies a lockless_dereference(), which provides the
protection for dereferences without the RCU-related debugging noise.
Reported-by: default avatarAl Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
[ luis: 3.16 prereq for:
  37868fe1 "x86/ldt: Make modify_ldt synchronous" ]
Signed-off-by: default avatarLuis Henriques <luis.henriques@canonical.com>
parent 2cf3a79d
...@@ -592,6 +592,21 @@ static inline void rcu_preempt_sleep_check(void) ...@@ -592,6 +592,21 @@ 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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