From: Thomas Gleixner <tglx@linutronix.de>

[ Upstream commit 82ed6f7ef58f9634fe4462dd721902c580f01569 ]

The timer code still has a few BUG_ON()s left which are crashing the kernel
in situations where it still can recover or simply refuse to take an
action.

Remove the one in the hotplug callback which checks for the CPU being
offline. If that happens then the whole hotplug machinery will explode in
colourful ways.

Replace the rest with WARN_ON_ONCE() and conditional returns where
appropriate.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Reviewed-by: Anna-Maria Behnsen <anna-maria@linutronix.de>
Link: https://lore.kernel.org/r/20221123201624.769128888@linutronix.de
Signed-off-by: Jeongjun Park <aha310510@gmail.com>
---
 kernel/time/timer.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index e09852be4e63..7094b916c854 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1208,7 +1208,8 @@ EXPORT_SYMBOL(timer_reduce);
  */
 void add_timer(struct timer_list *timer)
 {
-	BUG_ON(timer_pending(timer));
+	if (WARN_ON_ONCE(timer_pending(timer)))
+		return;
 	__mod_timer(timer, timer->expires, MOD_TIMER_NOTPENDING);
 }
 EXPORT_SYMBOL(add_timer);
@@ -1227,7 +1228,8 @@ void add_timer_on(struct timer_list *timer, int cpu)
 	struct timer_base *new_base, *base;
 	unsigned long flags;
 
-	BUG_ON(timer_pending(timer) || !timer->function);
+	if (WARN_ON_ONCE(timer_pending(timer) || !timer->function))
+		return;
 
 	new_base = get_timer_cpu_base(timer->flags, cpu);
 
@@ -2047,8 +2049,6 @@ int timers_dead_cpu(unsigned int cpu)
 	struct timer_base *new_base;
 	int b, i;
 
-	BUG_ON(cpu_online(cpu));
-
 	for (b = 0; b < NR_BASES; b++) {
 		old_base = per_cpu_ptr(&timer_bases[b], cpu);
 		new_base = get_cpu_ptr(&timer_bases[b]);
@@ -2065,7 +2065,8 @@ int timers_dead_cpu(unsigned int cpu)
 		 */
 		forward_timer_base(new_base);
 
-		BUG_ON(old_base->running_timer);
+		WARN_ON_ONCE(old_base->running_timer);
+		old_base->running_timer = NULL;
 
 		for (i = 0; i < WHEEL_SIZE; i++)
 			migrate_timer_list(new_base, old_base->vectors + i);
--