[tip: sched/core] sched,livepatch: Use wake_up_if_idle()

[tip-bot2 for Peter Zijlstra]

The following commit has been merged into the sched/core branch of tip:

Commit-ID:     5de62ea84abd732ded7c5569426fd71c0420f83e
Gitweb:        https://git.kernel.org/tip/5de62ea84abd732ded7c5569426fd71c0420f83e
Author:        Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate:    Tue, 21 Sep 2021 22:16:02 +02:00
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Thu, 14 Oct 2021 13:09:25 +02:00

sched,livepatch: Use wake_up_if_idle()

Make sure to prod idle CPUs so they call klp_update_patch_state().

Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Reviewed-by: Petr Mladek <pmladek@xxxxxxxx>
Acked-by: Miroslav Benes <mbenes@xxxxxxx>
Acked-by: Vasily Gorbik <gor@xxxxxxxxxxxxx>
Tested-by: Petr Mladek <pmladek@xxxxxxxx>
Tested-by: Vasily Gorbik <gor@xxxxxxxxxxxxx> # on s390
Link: https://lkml.kernel.org/r/20210929151723.162004989@xxxxxxxxxxxxx
---
 include/linux/sched/idle.h    | 4 ++++
 kernel/livepatch/transition.c | 5 ++++-
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/include/linux/sched/idle.h b/include/linux/sched/idle.h
index 22873d2..d73d314 100644
--- a/include/linux/sched/idle.h
+++ b/include/linux/sched/idle.h
@@ -11,7 +11,11 @@ enum cpu_idle_type {
 	CPU_MAX_IDLE_TYPES
 };
 
+#ifdef CONFIG_SMP
 extern void wake_up_if_idle(int cpu);
+#else
+static inline void wake_up_if_idle(int cpu) { }
+#endif
 
 /*
  * Idle thread specific functions to determine the need_resched
diff --git a/kernel/livepatch/transition.c b/kernel/livepatch/transition.c
index 75251e9..5683ac0 100644
--- a/kernel/livepatch/transition.c
+++ b/kernel/livepatch/transition.c
@@ -413,8 +413,11 @@ void klp_try_complete_transition(void)
 	for_each_possible_cpu(cpu) {
 		task = idle_task(cpu);
 		if (cpu_online(cpu)) {
-			if (!klp_try_switch_task(task))
+			if (!klp_try_switch_task(task)) {
 				complete = false;
+				/* Make idle task go through the main loop. */
+				wake_up_if_idle(cpu);
+			}
 		} else if (task->patch_state != klp_target_state) {
 			/* offline idle tasks can be switched immediately */
 			clear_tsk_thread_flag(task, TIF_PATCH_PENDING);