nohz: Ensure full dynticks CPUs are RCU nocbs

We need full dynticks CPU to also be RCU nocb so
that we don't have to keep the tick to handle RCU
callbacks.

Make sure the range passed to nohz_full= boot
parameter is a subset of rcu_nocbs=

The CPUs that fail to meet this requirement will be
excluded from the nohz_full range. This is checked
early in boot time, before any CPU has the opportunity
to stop its tick.

Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Chris Metcalf <cmetcalf@tilera.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: Geoff Levand <geoff@infradead.org>
Cc: Gilad Ben Yossef <gilad@benyossef.com>
Cc: Hakan Akkan <hakanakkan@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Kevin Hilman <khilman@linaro.org>
Cc: Li Zhong <zhong@linux.vnet.ibm.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 4 insertions, 9 deletions

diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index a5745e9b5d5a..0cd91cc18db4 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -2167,7 +2167,7 @@ static int __init parse_rcu_nocb_poll(char *arg)
 early_param("rcu_nocb_poll", parse_rcu_nocb_poll);
 
 /* Is the specified CPU a no-CPUs CPU? */
-static bool is_nocb_cpu(int cpu)
+bool rcu_is_nocb_cpu(int cpu)
 {
         if (have_rcu_nocb_mask)
                 return cpumask_test_cpu(cpu, rcu_nocb_mask);
@@ -2225,7 +2225,7 @@ static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
                             bool lazy)
 {
 
-        if (!is_nocb_cpu(rdp->cpu))
+        if (!rcu_is_nocb_cpu(rdp->cpu))
                 return 0;
         __call_rcu_nocb_enqueue(rdp, rhp, &rhp->next, 1, lazy);
         return 1;
@@ -2242,7 +2242,7 @@ static bool __maybe_unused rcu_nocb_adopt_orphan_cbs(struct rcu_state *rsp,
         long qll = rsp->qlen_lazy;
 
         /* If this is not a no-CBs CPU, tell the caller to do it the old way. */
-        if (!is_nocb_cpu(smp_processor_id()))
+        if (!rcu_is_nocb_cpu(smp_processor_id()))
                 return 0;
         rsp->qlen = 0;
         rsp->qlen_lazy = 0;
@@ -2282,7 +2282,7 @@ static bool nocb_cpu_expendable(int cpu)
          * If there are no no-CB CPUs or if this CPU is not a no-CB CPU,
          * then offlining this CPU is harmless.  Let it happen.
          */
-        if (!have_rcu_nocb_mask || is_nocb_cpu(cpu))
+        if (!have_rcu_nocb_mask || rcu_is_nocb_cpu(cpu))
                 return 1;
 
         /* If no memory, play it safe and keep the CPU around. */
@@ -2464,11 +2464,6 @@ static void __init rcu_init_nocb(void)
 
 #else /* #ifdef CONFIG_RCU_NOCB_CPU */
 
-static bool is_nocb_cpu(int cpu)
-{
-        return false;
-}
-
 static bool __call_rcu_nocb(struct rcu_data *rdp, struct rcu_head *rhp,
                             bool lazy)
 {