[RFC PATCH 18/18] cgroup/cpuset: Add pr_debug() statements for cpuhp_offline_cb() call

[Waiman Long]

Add some pr_debug() statements to actions performed related to the
cpuhp_offline_cb() call to aid debugging. Since rcu_nocb_cpu_offload()
and rcu_nocb_cpu_deoffload() will print out some info text, there is
no need to add pr_debug() statements for them.

Also update test_cpuset_prs.sh test script to enable printing of dynamic
debug messages for the kernel/cgroup/cpuset.c file when loglevel is 7
(debug).

Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
---
 kernel/cgroup/cpuset.c                         | 18 +++++++++++++-----
 .../selftests/cgroup/test_cpuset_prs.sh        |  7 +++++++
 2 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 489708f4e096..30632e4b5899 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -21,6 +21,7 @@
  *  License.  See the file COPYING in the main directory of the Linux
  *  distribution for more details.
  */
+#define pr_fmt(fmt) "cpuset: " fmt
 #include "cpuset-internal.h"
 
 #include <linux/context_tracking.h>
@@ -1406,10 +1407,13 @@ static int do_housekeeping_exclude_cpumask(void *arg __maybe_unused)
 	if (tick_nohz_full_enabled()) {
 		tick_nohz_full_update_cpus(icpus);
 		for_each_cpu(cpu, isolcpus_update_state.cpus) {
-			if (cpumask_test_cpu(cpu, icpus))
+			if (cpumask_test_cpu(cpu, icpus)) {
+				pr_debug("Add CPU %d to nohz_full\n", cpu);
 				ct_cpu_track_user(cpu);
-			else
+			} else {
+				pr_debug("Remove CPU %d from nohz_full\n", cpu);
 				ct_cpu_untrack_user(cpu);
+			}
 		}
 	} else {
 		pr_warn_once("Full dynticks cannot be enabled without the nohz_full kernel boot parameter!\n");
@@ -1425,6 +1429,7 @@ static int do_housekeeping_exclude_cpumask(void *arg __maybe_unused)
 				ret = rcu_nocb_cpu_offload(cpu);
 			else
 				ret = rcu_nocb_cpu_deoffload(cpu);
+
 			if (WARN_ON_ONCE(ret))
 				break;
 		}
@@ -1468,11 +1473,14 @@ static void update_isolation_cpumasks(void)
 	 * Without any change in the set of nohz_full CPUs, we don't really
 	 * need to use CPU hotplug for making change in HK cpumasks.
 	 */
-	if (cpumask_empty(isolcpus_update_state.cpus))
+	if (cpumask_empty(isolcpus_update_state.cpus)) {
 		ret = do_housekeeping_exclude_cpumask(NULL);
-	else
+	} else {
+		pr_debug("cpuhp_offline_cb() called for CPUs %*pbl\n",
+			 cpumask_pr_args(isolcpus_update_state.cpus));
 		ret = cpuhp_offline_cb(isolcpus_update_state.cpus,
 				       do_housekeeping_exclude_cpumask, NULL);
+	}
 	/*
 	 * A errno value of -EPERM may be returned from cpuhp_offline_cb() if
 	 * any one of the CPUs in isolcpus_update_state.cpus can't be brought
@@ -1481,7 +1489,7 @@ static void update_isolation_cpumasks(void)
 	 * isolated partition.
 	 */
 	if (ret == -EPERM)
-		pr_warn_once("cpuset: The boot CPU shouldn't be used for isolated partition\n");
+		pr_warn_once("The boot CPU shouldn't be used for isolated partition\n");
 	else
 		WARN_ON_ONCE(ret < 0);
 
diff --git a/tools/testing/selftests/cgroup/test_cpuset_prs.sh b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
index f61369be8bf6..43a12690775e 100755
--- a/tools/testing/selftests/cgroup/test_cpuset_prs.sh
+++ b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
@@ -67,6 +67,13 @@ then
 	echo Y > /sys/kernel/debug/sched/verbose
 fi
 
+# Enable dynamic debug messages for cpuset only
+DYN_DEBUG=/sys/kernel/debug/dynamic_debug/control
+[[ -f $DYN_DEBUG ]] && {
+	echo "-p" > $DYN_DEBUG
+	echo "file kernel/cgroup/cpuset.c +p" > $DYN_DEBUG
+}
+
 cd $CGROUP2
 echo +cpuset > cgroup.subtree_control
 
-- 
2.50.0