提交 f5155b33 编写于 作者: P Paul E. McKenney

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: NPaul E. McKenney <paulmck@linux.vnet.ibm.com>
上级 551d55a9
......@@ -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 */
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