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Commit f5155b33 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: add an rcu_dereference_index_check() 



The sparse RCU-pointer checking relies on type magic that dereferences
the pointer in question.  This does not work if the pointer is in fact
an array index.  This commit therefore supplies a new RCU API that
omits the sparse checking to continue to support rcu_dereference()
on integers.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent 551d55a9

include/linux/rcupdate.h

+33 −0
Original line number Diff line number Diff line
@@ -566,4 +566,37 @@ static inline void debug_rcu_head_unqueue(struct rcu_head *head) 
}

#endif	/* #else !CONFIG_DEBUG_OBJECTS_RCU_HEAD */



#ifndef CONFIG_PROVE_RCU

#define __do_rcu_dereference_check(c) do { } while (0)

#endif /* #ifdef CONFIG_PROVE_RCU */



#define __rcu_dereference_index_check(p, c) \

	({ \

		typeof(p) _________p1 = ACCESS_ONCE(p); \

		__do_rcu_dereference_check(c); \

		smp_read_barrier_depends(); \

		(_________p1); \

	})



/**

 * rcu_dereference_index_check() - rcu_dereference for indices with debug checking

 * @p: The pointer to read, prior to dereferencing

 * @c: The conditions under which the dereference will take place

 *

 * Similar to rcu_dereference_check(), but omits the sparse checking.

 * This allows rcu_dereference_index_check() to be used on integers,

 * which can then be used as array indices.  Attempting to use

 * rcu_dereference_check() on an integer will give compiler warnings

 * because the sparse address-space mechanism relies on dereferencing

 * the RCU-protected pointer.  Dereferencing integers is not something

 * that even gcc will put up with.

 *

 * Note that this function does not implicitly check for RCU read-side

 * critical sections.  If this function gains lots of uses, it might

 * make sense to provide versions for each flavor of RCU, but it does

 * not make sense as of early 2010.

 */

#define rcu_dereference_index_check(p, c) \

	__rcu_dereference_index_check((p), (c))



#endif /* __LINUX_RCUPDATE_H */