Patch "tick: Detect and fix jiffies update stall" has been added to the 5.10-stable tree

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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



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