The following commit has been merged into the timers/urgent branch of tip:
Commit-ID: 13bb06f8dd42071cb9a49f6e21099eea05d4b856 Gitweb: https://git.kernel.org/tip/13bb06f8dd42071cb9a49f6e21099eea05d4b856 Author: Thomas Gleixner tglx@linutronix.de AuthorDate: Thu, 15 Jun 2023 11:18:30 +02:00 Committer: Thomas Gleixner tglx@linutronix.de CommitterDate: Fri, 16 Jun 2023 20:45:28 +02:00
tick/common: Align tick period during sched_timer setup
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@grsecurity.net Reported-by: "Bhatnagar, Rishabh" risbhat@amazon.com Suggested-by: Mathias Krause minipli@grsecurity.net Signed-off-by: Thomas Gleixner tglx@linutronix.de Signed-off-by: Sebastian Andrzej Siewior bigeasy@linutronix.de Signed-off-by: Thomas Gleixner tglx@linutronix.de Tested-by: Richard W.M. Jones rjones@redhat.com Tested-by: Mathias Krause minipli@grsecurity.net Acked-by: SeongJae Park sj@kernel.org Cc: stable@vger.kernel.org Link: https://lore.kernel.org/5a56290d-806e-b9a5-f37c-f21958b5a8c0@grsecurity.net Link: https://lore.kernel.org/12c6f9a3-d087-b824-0d05-0d18c9bc1bf3@amazon.com Link: https://lore.kernel.org/r/20230615091830.RxMV2xf_@linutronix.de --- kernel/time/tick-common.c | 13 +------------ kernel/time/tick-sched.c | 13 ++++++++++++- 2 files changed, 13 insertions(+), 13 deletions(-)
diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c index 65b8658..e9138cd 100644 --- a/kernel/time/tick-common.c +++ b/kernel/time/tick-common.c @@ -218,19 +218,8 @@ static void tick_setup_device(struct tick_device *td, * 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 diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index 5225467..42c0be3 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -161,8 +161,19 @@ static ktime_t tick_init_jiffy_update(void) 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);