[PATCH 3/4] kernel/sched/isolation: require a present CPU in housekeeping mask

[Nicholas Piggin]

During housekeeping mask setup, currently a possible CPU is required.
That does not guarantee a CPU at boot time, so check to ensure that
at least one present CPU is in the mask.

Signed-off-by: Nicholas Piggin <npiggin@xxxxxxxxx>
---
 kernel/sched/isolation.c | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
index b02d148e7672..687302051a27 100644
--- a/kernel/sched/isolation.c
+++ b/kernel/sched/isolation.c
@@ -65,6 +65,7 @@ void __init housekeeping_init(void)
 static int __init housekeeping_setup(char *str, enum hk_flags flags)
 {
 	cpumask_var_t non_housekeeping_mask;
+	cpumask_var_t tmp;
 	int err;
 
 	alloc_bootmem_cpumask_var(&non_housekeeping_mask);
@@ -75,16 +76,23 @@ static int __init housekeeping_setup(char *str, enum hk_flags flags)
 		return 0;
 	}
 
+	alloc_bootmem_cpumask_var(&tmp);
 	if (!housekeeping_flags) {
 		alloc_bootmem_cpumask_var(&housekeeping_mask);
 		cpumask_andnot(housekeeping_mask,
 			       cpu_possible_mask, non_housekeeping_mask);
-		if (cpumask_empty(housekeeping_mask))
+
+		cpumask_andnot(tmp, cpu_present_mask, non_housekeeping_mask);
+		if (cpumask_empty(tmp)) {
+			pr_warn("Housekeeping: must include one present CPU, "
+				"using boot CPU:%d\n", smp_processor_id());
 			__cpumask_set_cpu(smp_processor_id(), housekeeping_mask);
+			__cpumask_clear_cpu(smp_processor_id(), non_housekeeping_mask);
+		}
 	} else {
-		cpumask_var_t tmp;
-
-		alloc_bootmem_cpumask_var(&tmp);
+		cpumask_andnot(tmp, cpu_present_mask, non_housekeeping_mask);
+		if (cpumask_empty(tmp))
+			__cpumask_clear_cpu(smp_processor_id(), non_housekeeping_mask);
 		cpumask_andnot(tmp, cpu_possible_mask, non_housekeeping_mask);
 		if (!cpumask_equal(tmp, housekeeping_mask)) {
 			pr_warn("Housekeeping: nohz_full= must match isolcpus=\n");
@@ -92,8 +100,8 @@ static int __init housekeeping_setup(char *str, enum hk_flags flags)
 			free_bootmem_cpumask_var(non_housekeeping_mask);
 			return 0;
 		}
-		free_bootmem_cpumask_var(tmp);
 	}
+	free_bootmem_cpumask_var(tmp);
 
 	if ((flags & HK_FLAG_TICK) && !(housekeeping_flags & HK_FLAG_TICK)) {
 		if (IS_ENABLED(CONFIG_NO_HZ_FULL)) {
-- 
2.20.1