[PATCH 3/3] smpboot: Don't park the thread if work is pending

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

Once a smpboot thread gets work assigned it receives a wake up. If the
thread had no chance to run and receives a parking requesst during a
CPU-hotplug event then it is parked without running the callback first.
As a result the enqueued work remains stuck until the CPU gets back
online.

There is nothing wrong with invoking the thread function first and
parking in the following iteration. This would ensure that the callbacks
are processed before the shutdown.

Honor the park request once thread function does not need to run.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
 kernel/smpboot.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/smpboot.c b/kernel/smpboot.c
index 4503b60ce9bd2..3f60e8c6dd301 100644
--- a/kernel/smpboot.c
+++ b/kernel/smpboot.c
@@ -103,6 +103,7 @@ static int smpboot_thread_fn(void *data)
 {
 	struct smpboot_thread_data *td = data;
 	struct smp_hotplug_thread *ht = td->ht;
+	bool should_run;
 
 	while (1) {
 		set_current_state(TASK_INTERRUPTIBLE);
@@ -117,7 +118,8 @@ static int smpboot_thread_fn(void *data)
 			return 0;
 		}
 
-		if (kthread_should_park()) {
+		should_run = td->status == HP_THREAD_ACTIVE && ht->thread_should_run(td->cpu);
+		if (kthread_should_park() && !should_run) {
 			__set_current_state(TASK_RUNNING);
 			preempt_enable();
 			if (ht->park && td->status == HP_THREAD_ACTIVE) {
@@ -151,7 +153,7 @@ static int smpboot_thread_fn(void *data)
 			continue;
 		}
 
-		if (!ht->thread_should_run(td->cpu)) {
+		if (!should_run) {
 			preempt_enable_no_resched();
 			schedule();
 		} else {
-- 
2.55.0