rcu: Clarify role of ->expmaskinitnext

Analogy with the ->qsmaskinitnext field might lead one to believe that
->expmaskinitnext tracks online CPUs.  This belief is incorrect: Any CPU
that has ever been online will have its bit set in the ->expmaskinitnext
field.  This commit therefore adds a comment to make this clear, at
least to people who read comments.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index f32bebb..8151971 100644 (file)
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -178,6 +178,8 @@ struct rcu_node {
                                /*  beginning of each expedited GP. */
        unsigned long expmaskinitnext;
                                /* Online CPUs for next expedited GP. */
+                               /*  Any CPU that has ever been online will */
+                               /*  have its bit set. */
        unsigned long grpmask;  /* Mask to apply to parent qsmask. */
                                /*  Only one bit will be set in this mask. */
        int     grplo;          /* lowest-numbered CPU or group here. */