From a4dd99250dc49031e6a92a895dbcc230a4832083 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Fri, 1 Apr 2011 07:15:14 -0700 Subject: rcu: create new rcu_access_index() and use in mce The MCE subsystem needs to sample an RCU-protected index outside of any protection for that index. If this was a pointer, we would use rcu_access_pointer(), but there is no corresponding rcu_access_index(). This commit therefore creates an rcu_access_index() and applies it to MCE. Signed-off-by: Paul E. McKenney Tested-by: Zdenek Kabelac --- include/linux/rcupdate.h | 20 ++++++++++++++++++++ 1 file changed, 20 insertions(+) (limited to 'include') diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index af561485628..ff422d2b7f9 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -339,6 +339,12 @@ extern int rcu_my_thread_group_empty(void); ((typeof(*p) __force __kernel *)(p)); \ }) +#define __rcu_access_index(p, space) \ + ({ \ + typeof(p) _________p1 = ACCESS_ONCE(p); \ + rcu_dereference_sparse(p, space); \ + (_________p1); \ + }) #define __rcu_dereference_index_check(p, c) \ ({ \ typeof(p) _________p1 = ACCESS_ONCE(p); \ @@ -428,6 +434,20 @@ extern int rcu_my_thread_group_empty(void); #define rcu_dereference_raw(p) rcu_dereference_check(p, 1) /*@@@ needed? @@@*/ +/** + * rcu_access_index() - fetch RCU index with no dereferencing + * @p: The index to read + * + * Return the value of the specified RCU-protected index, but omit the + * smp_read_barrier_depends() and keep the ACCESS_ONCE(). This is useful + * when the value of this index is accessed, but the index is not + * dereferenced, for example, when testing an RCU-protected index against + * -1. Although rcu_access_index() may also be used in cases where + * update-side locks prevent the value of the index from changing, you + * should instead use rcu_dereference_index_protected() for this use case. + */ +#define rcu_access_index(p) __rcu_access_index((p), __rcu) + /** * rcu_dereference_index_check() - rcu_dereference for indices with debug checking * @p: The pointer to read, prior to dereferencing -- cgit v1.2.3-70-g09d2