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-rw-r--r--kernel/rcupdate.c18
1 files changed, 13 insertions, 5 deletions
diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c
index f45b91723dc6..48d3bce465b8 100644
--- a/kernel/rcupdate.c
+++ b/kernel/rcupdate.c
@@ -257,15 +257,23 @@ static void rcu_start_batch(struct rcu_ctrlblk *rcp, struct rcu_state *rsp,
if (rcp->next_pending &&
rcp->completed == rcp->cur) {
- /* Can't change, since spin lock held. */
- cpus_andnot(rsp->cpumask, cpu_online_map, nohz_cpu_mask);
-
rcp->next_pending = 0;
- /* next_pending == 0 must be visible in __rcu_process_callbacks()
- * before it can see new value of cur.
+ /*
+ * next_pending == 0 must be visible in
+ * __rcu_process_callbacks() before it can see new value of cur.
*/
smp_wmb();
rcp->cur++;
+
+ /*
+ * Accessing nohz_cpu_mask before incrementing rcp->cur needs a
+ * Barrier Otherwise it can cause tickless idle CPUs to be
+ * included in rsp->cpumask, which will extend graceperiods
+ * unnecessarily.
+ */
+ smp_mb();
+ cpus_andnot(rsp->cpumask, cpu_online_map, nohz_cpu_mask);
+
}
}