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

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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: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Paul E. McKenney 2014-10-27 21:11:27 -07:00 • committed by Al Viro
commit 54ef6df3f3
1 changed files with 15 additions and 0 deletions
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15
include/linux/rcupdate.h
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@ -616,6 +616,21 @@ 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