[PATCH 2/4] kernel/cpu: Allow non-zero CPU to be primary for suspend / kexec freeze

[Nicholas Piggin]

This patch chooses a housekeeping CPU to be the primary when disabling
CPUs for suspend / kexec freeze. This should not have any effect until
a later change because CPU0 is always a housekeeping CPU.

Signed-off-by: Nicholas Piggin <npig...@gmail.com>
---
 include/linux/cpu.h |  2 +-
 kernel/cpu.c        | 10 +++++++++-
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/include/linux/cpu.h b/include/linux/cpu.h
index 5041357d0297..b11c94d88953 100644
--- a/include/linux/cpu.h
+++ b/include/linux/cpu.h
@@ -134,7 +134,7 @@ static inline void put_online_cpus(void) { 
cpus_read_unlock(); }
 extern int freeze_secondary_cpus(int primary);
 static inline int disable_nonboot_cpus(void)
 {
-       return freeze_secondary_cpus(0);
+       return freeze_secondary_cpus(-1);
 }
 extern void enable_nonboot_cpus(void);
 #else /* !CONFIG_PM_SLEEP_SMP */
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 6754f3ecfd94..d1bf6e2b4752 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -9,6 +9,7 @@
 #include <linux/notifier.h>
 #include <linux/sched/signal.h>
 #include <linux/sched/hotplug.h>
+#include <linux/sched/isolation.h>
 #include <linux/sched/task.h>
 #include <linux/sched/smt.h>
 #include <linux/unistd.h>
@@ -1199,8 +1200,15 @@ int freeze_secondary_cpus(int primary)
        int cpu, error = 0;
 
        cpu_maps_update_begin();
-       if (!cpu_online(primary))
+       if (primary == -1) {
                primary = cpumask_first(cpu_online_mask);
+               if (!housekeeping_cpu(primary, HK_FLAG_TIMER))
+                       primary = housekeeping_any_cpu(HK_FLAG_TIMER);
+       } else {
+               if (!cpu_online(primary))
+                       primary = cpumask_first(cpu_online_mask);
+       }
+
        /*
         * We take down all of the non-boot CPUs in one shot to avoid races
         * with the userspace trying to use the CPU hotplug at the same time
-- 
2.20.1