[PATCH] timers: Clear pending_map on CPU hotplug

[Liang Hao <haohlliang@gmail.com>]

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(), and in timers_prepare_cpu() for a full base reinit.

Signed-off-by: Liang Hao <haohlliang@gmail.com>
---
 kernel/time/timer.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/time/timer.c b/kernel/time/timer.c
index ae9abf14688e..e550489c73b8 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>
@@ -2509,6 +2510,7 @@ int timers_prepare_cpu(unsigned int cpu)
 		base->next_expiry_recalc = false;
 		base->timers_pending = false;
 		base->is_idle = false;
+		bitmap_zero(base->pending_map, WHEEL_SIZE);
 	}
 	return 0;
 }
@@ -2541,6 +2543,7 @@ 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);
-- 
2.50.1 (Apple Git-155)