[tip: timers/urgent] timers: Clear pending_map on CPU hotplug

[tip-bot2 for Liang Hao]

The following commit has been merged into the timers/urgent branch of tip:

Commit-ID:     e7cad586d73276cbd4466de81b2092287d7475c0
Gitweb:        https://git.kernel.org/tip/e7cad586d73276cbd4466de81b2092287d7475c0
Author:        Liang Hao <haohlliang@xxxxxxxxx>
AuthorDate:    Wed, 30 Sep 2026 14:36:21 +08:00
Committer:     Thomas Gleixner <tglx@xxxxxxxxxx>
CommitterDate: Tue, 20 Oct 2026 15:28:14 +02:00

timers: Clear pending_map on CPU hotplug

CPU hotplug migration leaves pending_map bits set on the outgoing CPU
while its wheel vectors are empty. After re-online, a later next_expiry
recalc can treat those empty buckets as pending and temporarily pull
next_expiry forward until collect drains the bits.

Clear pending_map under the base lock after migration in timers_dead_cpu().

Fixes: 500462a9de65 ("timers: Switch to a non-cascading wheel")
Signed-off-by: Liang Hao <haohlliang@xxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxx>
Link: https://patch.msgid.link/20260930063621.37740-1-haohlliang@xxxxxxxxx
---
 kernel/time/timer.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index ae9abf1..fc37444 100644
--- a/kernel/time/timer.c
+++ b/kernel/time/timer.c
@@ -44,6 +44,7 @@
 #include <linux/compat.h>
 #include <linux/random.h>
 #include <linux/sysctl.h>
+#include <linux/bitmap.h>
 
 #include <linux/uaccess.h>
 #include <asm/unistd.h>
@@ -2541,6 +2542,7 @@ int timers_dead_cpu(unsigned int cpu)
 		for (i = 0; i < WHEEL_SIZE; i++)
 			migrate_timer_list(new_base, old_base->vectors + i);
 
+		bitmap_zero(old_base->pending_map, WHEEL_SIZE);
 		raw_spin_unlock(&old_base->lock);
 		raw_spin_unlock_irq(&new_base->lock);
 		put_cpu_ptr(&timer_bases);