The patch titled
add rcu_assign_index() if ever needed
has been added to the -mm tree. Its filename is
add-rcu_assign_index-if-ever-needed.patch
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------------------------------------------------------
Subject: add rcu_assign_index() if ever needed
From: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxxxxxxx>
This is a speculative patch that as far as I can tell is not yet required.
If anyone applies RCU to a data structure allocated out of an array, using
array indexes in place of pointers to link the array elements together,
then the rcu_assign_index() function in this patch will be needed to assign
a given element's array index to the RCU-traversed index. The
implementation is exactly that of the old rcu_assign_pointer(), so is
extremely well tested.
The existing rcu_assign_pointer() will emit a compiler warning in cases
where rcu_assign_index() is required.
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/linux/rcupdate.h | 18 ++++++++++++++++++
1 file changed, 18 insertions(+)
diff -puN include/linux/rcupdate.h~add-rcu_assign_index-if-ever-needed include/linux/rcupdate.h
--- a/include/linux/rcupdate.h~add-rcu_assign_index-if-ever-needed
+++ a/include/linux/rcupdate.h
@@ -188,6 +188,24 @@ struct rcu_head {
})
/**
+ * rcu_assign_index - assign (publicize) a index of a newly
+ * initialized array elementg that will be dereferenced by RCU
+ * read-side critical sections. Returns the value assigned.
+ *
+ * Inserts memory barriers on architectures that require them
+ * (pretty much all of them other than x86), and also prevents
+ * the compiler from reordering the code that initializes the
+ * structure after the index assignment. More importantly, this
+ * call documents which indexes will be dereferenced by RCU read-side
+ * code.
+ */
+
+#define rcu_assign_index(p, v) ({ \
+ smp_wmb(); \
+ (p) = (v); \
+ })
+
+/**
* synchronize_sched - block until all CPUs have exited any non-preemptive
* kernel code sequences.
*
_
Patches currently in -mm which might be from paulmck@xxxxxxxxxxxxxxxxxx are
rcupdate-fix-comment.patch
remove-rcu_assign_pointernull-penalty-with-type-macro-safety.patch
add-rcu_assign_index-if-ever-needed.patch
git-sched.patch
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