srcu: Make srcu_funnel_gp_start() cache ->mynode in snp_leaf

Currently, the srcu_funnel_gp_start() walks its local variable snp up the
tree and reloads sdp->mynode whenever it is necessary to check whether
it is still at the leaf srcu_node level.  This works, but is a bit more
obtuse than absolutely necessary.  In addition, upcoming commits will
dynamically size srcu_struct structures, in which case sdp->mynode will
no longer necessarily be a constant, and this commit helps prepare for
that dynamic sizing.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index d30e4db04506a16068c920f5b7291a7070b72428..7d13e35e5d277ca12645e6b2af6c615b5030f372 100644 (file)
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -632,20 +632,21 @@ static void srcu_funnel_gp_start(struct srcu_struct *ssp, struct srcu_data *sdp,
 {
        unsigned long flags;
        int idx = rcu_seq_ctr(s) % ARRAY_SIZE(sdp->mynode->srcu_have_cbs);
-       struct srcu_node *snp = sdp->mynode;
+       struct srcu_node *snp;
+       struct srcu_node *snp_leaf = sdp->mynode;
        unsigned long snp_seq;
 
        /* Each pass through the loop does one level of the srcu_node tree. */
-       for (; snp != NULL; snp = snp->srcu_parent) {
-               if (rcu_seq_done(&ssp->srcu_gp_seq, s) && snp != sdp->mynode)
+       for (snp = snp_leaf; snp != NULL; snp = snp->srcu_parent) {
+               if (rcu_seq_done(&ssp->srcu_gp_seq, s) && snp != snp_leaf)
                        return; /* GP already done and CBs recorded. */
                spin_lock_irqsave_rcu_node(snp, flags);
                if (ULONG_CMP_GE(snp->srcu_have_cbs[idx], s)) {
                        snp_seq = snp->srcu_have_cbs[idx];
-                       if (snp == sdp->mynode && snp_seq == s)
+                       if (snp == snp_leaf && snp_seq == s)
                                snp->srcu_data_have_cbs[idx] |= sdp->grpmask;
                        spin_unlock_irqrestore_rcu_node(snp, flags);
-                       if (snp == sdp->mynode && snp_seq != s) {
+                       if (snp == snp_leaf && snp_seq != s) {
                                srcu_schedule_cbs_sdp(sdp, do_norm
                                                           ? SRCU_INTERVAL
                                                           : 0);
@@ -656,7 +657,7 @@ static void srcu_funnel_gp_start(struct srcu_struct *ssp, struct srcu_data *sdp,
                        return;
                }
                snp->srcu_have_cbs[idx] = s;
-               if (snp == sdp->mynode)
+               if (snp == snp_leaf)
                        snp->srcu_data_have_cbs[idx] |= sdp->grpmask;
                if (!do_norm && ULONG_CMP_LT(snp->srcu_gp_seq_needed_exp, s))
                        WRITE_ONCE(snp->srcu_gp_seq_needed_exp, s);