[PATCH tip/core/rcu 05/17] rcutorture: Affinity forward-progress test to avoid housekeeping CPUs

["Paul E. McKenney" <paulmck@linux.ibm.com>]

This commit affinities the forward-progress tests to avoid hogging a
housekeeping CPU on the theory that the offloaded callbacks will be
running on those housekeeping CPUs.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
[ paulmck: Fix NULL-pointer issue located by kbuild test robot. ]
Tested-by: Rong Chen <rong.a.chen@intel.com>
---
 kernel/rcu/rcu.h         |  2 ++
 kernel/rcu/rcutorture.c  |  1 +
 kernel/rcu/tree_plugin.h | 11 +++++++++++
 3 files changed, 14 insertions(+)

diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
index 2866166863f0..0f0f5ae8c3d4 100644
--- a/kernel/rcu/rcu.h
+++ b/kernel/rcu/rcu.h
@@ -539,8 +539,10 @@ extern struct workqueue_struct *rcu_par_gp_wq;
 
 #ifdef CONFIG_RCU_NOCB_CPU
 bool rcu_is_nocb_cpu(int cpu);
+void rcu_bind_current_to_nocb(void);
 #else
 static inline bool rcu_is_nocb_cpu(int cpu) { return false; }
+static inline void rcu_bind_current_to_nocb(void) { }
 #endif
 
 #endif /* __LINUX_RCU_H */
diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index bcc33bb8d9a6..36a3bc42782d 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -1803,6 +1803,7 @@ static int rcu_torture_fwd_prog(void *args)
 	int tested_tries = 0;
 
 	VERBOSE_TOROUT_STRING("rcu_torture_fwd_progress task started");
+	rcu_bind_current_to_nocb();
 	if (!IS_ENABLED(CONFIG_SMP) || !IS_ENABLED(CONFIG_RCU_BOOST))
 		set_user_nice(current, MAX_NICE);
 	do {
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 05915e536336..1db2b0780c62 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -2587,6 +2587,17 @@ static bool init_nocb_callback_list(struct rcu_data *rdp)
 	return true;
 }
 
+/*
+ * Bind the current task to the offloaded CPUs.  If there are no offloaded
+ * CPUs, leave the task unbound.  Splat if the bind attempt fails.
+ */
+void rcu_bind_current_to_nocb(void)
+{
+	if (cpumask_available(rcu_nocb_mask) && cpumask_weight(rcu_nocb_mask))
+		WARN_ON(sched_setaffinity(current->pid, rcu_nocb_mask));
+}
+EXPORT_SYMBOL_GPL(rcu_bind_current_to_nocb);
+
 #else /* #ifdef CONFIG_RCU_NOCB_CPU */
 
 static bool rcu_nocb_cpu_needs_barrier(int cpu)
-- 
2.17.1