This is a note to let you know that I've just added the patch titled
tick/common: Align tick period during sched_timer setup
to the 5.4-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-common-align-tick-period-during-sched_timer-setup.patch
and it can be found in the queue-5.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 13bb06f8dd42071cb9a49f6e21099eea05d4b856 Mon Sep 17 00:00:00 2001
From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Date: Thu, 15 Jun 2023 11:18:30 +0200
Subject: tick/common: Align tick period during sched_timer setup
From: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
commit 13bb06f8dd42071cb9a49f6e21099eea05d4b856 upstream.
The tick period is aligned very early while the first clock_event_device is
registered. At that point the system runs in periodic mode and switches
later to one-shot mode if possible.
The next wake-up event is programmed based on the aligned value
(tick_next_period) but the delta value, that is used to program the
clock_event_device, is computed based on ktime_get().
With the subtracted offset, the device fires earlier than the exact time
frame. With a large enough offset the system programs the timer for the
next wake-up and the remaining time left is too small to make any boot
progress. The system hangs.
Move the alignment later to the setup of tick_sched timer. At this point
the system switches to oneshot mode and a high resolution clocksource is
available. At this point it is safe to align tick_next_period because
ktime_get() will now return accurate (not jiffies based) time.
[bigeasy: Patch description + testing].
Fixes: e9523a0d81899 ("tick/common: Align tick period with the HZ tick.")
Reported-by: Mathias Krause <minipli@xxxxxxxxxxxxxx>
Reported-by: "Bhatnagar, Rishabh" <risbhat@xxxxxxxxxx>
Suggested-by: Mathias Krause <minipli@xxxxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Tested-by: Richard W.M. Jones <rjones@xxxxxxxxxx>
Tested-by: Mathias Krause <minipli@xxxxxxxxxxxxxx>
Acked-by: SeongJae Park <sj@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: https://lore.kernel.org/5a56290d-806e-b9a5-f37c-f21958b5a8c0@xxxxxxxxxxxxxx
Link: https://lore.kernel.org/12c6f9a3-d087-b824-0d05-0d18c9bc1bf3@xxxxxxxxxx
Link: https://lore.kernel.org/r/20230615091830.RxMV2xf_@xxxxxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/time/tick-common.c | 13 +------------
kernel/time/tick-sched.c | 13 ++++++++++++-
2 files changed, 13 insertions(+), 13 deletions(-)
--- a/kernel/time/tick-common.c
+++ b/kernel/time/tick-common.c
@@ -216,19 +216,8 @@ static void tick_setup_device(struct tic
* this cpu:
*/
if (tick_do_timer_cpu == TICK_DO_TIMER_BOOT) {
- ktime_t next_p;
- u32 rem;
-
tick_do_timer_cpu = cpu;
-
- next_p = ktime_get();
- div_u64_rem(next_p, TICK_NSEC, &rem);
- if (rem) {
- next_p -= rem;
- next_p += TICK_NSEC;
- }
-
- tick_next_period = next_p;
+ tick_next_period = ktime_get();
#ifdef CONFIG_NO_HZ_FULL
/*
* The boot CPU may be nohz_full, in which case set
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -129,8 +129,19 @@ static ktime_t tick_init_jiffy_update(vo
raw_spin_lock(&jiffies_lock);
write_seqcount_begin(&jiffies_seq);
/* Did we start the jiffies update yet ? */
- if (last_jiffies_update == 0)
+ if (last_jiffies_update == 0) {
+ u32 rem;
+
+ /*
+ * Ensure that the tick is aligned to a multiple of
+ * TICK_NSEC.
+ */
+ div_u64_rem(tick_next_period, TICK_NSEC, &rem);
+ if (rem)
+ tick_next_period += TICK_NSEC - rem;
+
last_jiffies_update = tick_next_period;
+ }
period = last_jiffies_update;
write_seqcount_end(&jiffies_seq);
raw_spin_unlock(&jiffies_lock);
Patches currently in stable-queue which might be from tglx@xxxxxxxxxxxxx are
queue-5.4/x86-purgatory-remove-pgo-flags.patch
queue-5.4/tick-common-align-tick-period-during-sched_timer-setup.patch
