Patch "timers: Replace BUG_ON()s" has been added to the 5.15-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    timers: Replace BUG_ON()s

to the 5.15-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     timers-replace-bug_on-s.patch
and it can be found in the queue-5.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


From stable+bounces-197608-greg=kroah.com@vger.kernel.org Fri Nov 28 17:08:07 2025
From: Jeongjun Park <aha310510@gmail.com>
Date: Sat, 29 Nov 2025 01:05:31 +0900
Subject: timers: Replace BUG_ON()s
To: stable@vger.kernel.org
Cc: gregkh@linuxfoundation.org, tglx@linutronix.de, Julia.Lawall@inria.fr, akpm@linux-foundation.org, anna-maria@linutronix.de, arnd@arndb.de, linux-bluetooth@vger.kernel.org, linux-kernel@vger.kernel.org, linux@roeck-us.net, luiz.dentz@gmail.com, marcel@holtmann.org, maz@kernel.org, peterz@infradead.org, rostedt@goodmis.org, sboyd@kernel.org, viresh.kumar@linaro.org, aha310510@gmail.com, linux-staging@lists.linux.dev, Jacob Keller <jacob.e.keller@intel.com>
Message-ID: <20251128160539.358938-7-aha310510@gmail.com>

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 kernel/time/timer.c |   11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -1155,7 +1155,8 @@ 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);
@@ -1174,7 +1175,8 @@ void add_timer_on(struct timer_list *tim
 	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);
 
@@ -1995,8 +1997,6 @@ 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]);
@@ -2013,7 +2013,8 @@ 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);


Patches currently in stable-queue which might be from aha310510@gmail.com are

queue-5.15/timers-update-the-documentation-to-reflect-on-the-new-timer_shutdown-api.patch
queue-5.15/clocksource-drivers-arm_arch_timer-do-not-use-timer-namespace-for-timer_shutdown-function.patch
queue-5.15/timers-split-del_timer-to-prepare-for-shutdown-mode.patch
queue-5.15/arm-spear-do-not-use-timer-namespace-for-timer_shutdown-function.patch
queue-5.15/timers-add-shutdown-mechanism-to-the-internal-functions.patch
queue-5.15/timers-provide-timer_shutdown.patch
queue-5.15/timers-rename-del_timer-to-timer_delete.patch
queue-5.15/timers-replace-bug_on-s.patch
queue-5.15/bluetooth-hci_qca-fix-the-teardown-problem-for-real.patch
queue-5.15/documentation-replace-del_timer-del_timer_sync.patch
queue-5.15/documentation-remove-bogus-claim-about-del_timer_sync.patch
queue-5.15/timers-silently-ignore-timers-with-a-null-function.patch
queue-5.15/timers-get-rid-of-del_singleshot_timer_sync.patch
queue-5.15/clocksource-drivers-sp804-do-not-use-timer-namespace-for-timer_shutdown-function.patch