[RFC 2/5] rcu: Use leaf_node_for_each_mask_possible_cpu() in RCU stall checking

[Boqun Feng]

Replace for_each_leaf_node_possible_cpu() loop with
leaf_node_for_each_mask_possible_cpu() loop to gain fewer checks in RCU
stall checking code.

Signed-off-by: Boqun Feng <boqun.f...@gmail.com>
---
 kernel/rcu/tree.c | 23 ++++++++++++-----------
 1 file changed, 12 insertions(+), 11 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index b56e2dc31ba5..5f6802b9ba5f 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1412,15 +1412,16 @@ static void rcu_check_gp_kthread_starvation(struct 
rcu_state *rsp)
 static void rcu_dump_cpu_stacks(struct rcu_state *rsp)
 {
        int cpu;
-       unsigned long flags;
+       unsigned long flags, bit;
        struct rcu_node *rnp;
 
        rcu_for_each_leaf_node(rsp, rnp) {
                raw_spin_lock_irqsave_rcu_node(rnp, flags);
-               for_each_leaf_node_possible_cpu(rnp, cpu)
-                       if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu))
-                               if (!trigger_single_cpu_backtrace(cpu))
-                                       dump_cpu_task(cpu);
+
+               leaf_node_for_each_mask_possible_cpu(rnp, rnp->qsmask, bit, cpu)
+                       if (!trigger_single_cpu_backtrace(cpu))
+                               dump_cpu_task(cpu);
+
                raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
        }
 }
@@ -1455,6 +1456,7 @@ static void print_other_cpu_stall(struct rcu_state *rsp, 
unsigned long gpnum)
 {
        int cpu;
        long delta;
+       unsigned long bit;
        unsigned long flags;
        unsigned long gpa;
        unsigned long j;
@@ -1490,13 +1492,12 @@ static void print_other_cpu_stall(struct rcu_state 
*rsp, unsigned long gpnum)
        rcu_for_each_leaf_node(rsp, rnp) {
                raw_spin_lock_irqsave_rcu_node(rnp, flags);
                ndetected += rcu_print_task_stall(rnp);
-               if (rnp->qsmask != 0) {
-                       for_each_leaf_node_possible_cpu(rnp, cpu)
-                               if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu)) {
-                                       print_cpu_stall_info(rsp, cpu);
-                                       ndetected++;
-                               }
+
+               leaf_node_for_each_mask_possible_cpu(rnp, rnp->qsmask, bit, 
cpu) {
+                       print_cpu_stall_info(rsp, cpu);
+                       ndetected++;
                }
+
                raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
        }
 
-- 
2.10.2