This is a note to let you know that I've just added the patch titled
tick: Detect and fix jiffies update stall
to the 5.10-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:
tick-detect-and-fix-jiffies-update-stall.patch
and it can be found in the queue-5.10 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From a1ff03cd6fb9c501fff63a4a2bface9adcfa81cd Mon Sep 17 00:00:00 2001
From: Frederic Weisbecker <frederic@xxxxxxxxxx>
Date: Wed, 2 Feb 2022 01:01:07 +0100
Subject: tick: Detect and fix jiffies update stall
From: Frederic Weisbecker <frederic@xxxxxxxxxx>
commit a1ff03cd6fb9c501fff63a4a2bface9adcfa81cd upstream.
On some rare cases, the timekeeper CPU may be delaying its jiffies
update duty for a while. Known causes include:
* The timekeeper is waiting on stop_machine in a MULTI_STOP_DISABLE_IRQ
or MULTI_STOP_RUN state. Disabled interrupts prevent from timekeeping
updates while waiting for the target CPU to complete its
stop_machine() callback.
* The timekeeper vcpu has VMEXIT'ed for a long while due to some overload
on the host.
Detect and fix these situations with emergency timekeeping catchups.
Original-patch-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Signed-off-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/time/tick-sched.c | 17 +++++++++++++++++
kernel/time/tick-sched.h | 4 ++++
2 files changed, 21 insertions(+)
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -148,6 +148,8 @@ static ktime_t tick_init_jiffy_update(vo
return period;
}
+#define MAX_STALLED_JIFFIES 5
+
static void tick_sched_do_timer(struct tick_sched *ts, ktime_t now)
{
int cpu = smp_processor_id();
@@ -175,6 +177,21 @@ static void tick_sched_do_timer(struct t
if (tick_do_timer_cpu == cpu)
tick_do_update_jiffies64(now);
+ /*
+ * If jiffies update stalled for too long (timekeeper in stop_machine()
+ * or VMEXIT'ed for several msecs), force an update.
+ */
+ if (ts->last_tick_jiffies != jiffies) {
+ ts->stalled_jiffies = 0;
+ ts->last_tick_jiffies = READ_ONCE(jiffies);
+ } else {
+ if (++ts->stalled_jiffies == MAX_STALLED_JIFFIES) {
+ tick_do_update_jiffies64(now);
+ ts->stalled_jiffies = 0;
+ ts->last_tick_jiffies = READ_ONCE(jiffies);
+ }
+ }
+
if (ts->inidle)
ts->got_idle_tick = 1;
}
--- a/kernel/time/tick-sched.h
+++ b/kernel/time/tick-sched.h
@@ -49,6 +49,8 @@ enum tick_nohz_mode {
* @timer_expires_base: Base time clock monotonic for @timer_expires
* @next_timer: Expiry time of next expiring timer for debugging purpose only
* @tick_dep_mask: Tick dependency mask - is set, if someone needs the tick
+ * @last_tick_jiffies: Value of jiffies seen on last tick
+ * @stalled_jiffies: Number of stalled jiffies detected across ticks
*/
struct tick_sched {
struct hrtimer sched_timer;
@@ -77,6 +79,8 @@ struct tick_sched {
u64 next_timer;
ktime_t idle_expires;
atomic_t tick_dep_mask;
+ unsigned long last_tick_jiffies;
+ unsigned int stalled_jiffies;
};
extern struct tick_sched *tick_get_tick_sched(int cpu);
Patches currently in stable-queue which might be from frederic@xxxxxxxxxx are
queue-5.10/tick-detect-and-fix-jiffies-update-stall.patch
