From e9523a0d81899361214d118ad60ef76f0e92f71d Mon Sep 17 00:00:00 2001 From: Sebastian Andrzej Siewior Date: Tue, 18 Apr 2023 14:26:39 +0200 Subject: tick/common: Align tick period with the HZ tick. With HIGHRES enabled tick_sched_timer() is programmed every jiffy to expire the timer_list timers. This timer is programmed accurate in respect to CLOCK_MONOTONIC so that 0 seconds and nanoseconds is the first tick and the next one is 1000/CONFIG_HZ ms later. For HZ=250 it is every 4 ms and so based on the current time the next tick can be computed. This accuracy broke since the commit mentioned below because the jiffy based clocksource is initialized with higher accuracy in read_persistent_wall_and_boot_offset(). This higher accuracy is inherited during the setup in tick_setup_device(). The timer still fires every 4ms with HZ=250 but timer is no longer aligned with CLOCK_MONOTONIC with 0 as it origin but has an offset in the us/ns part of the timestamp. The offset differs with every boot and makes it impossible for user land to align with the tick. Align the tick period with CLOCK_MONOTONIC ensuring that it is always a multiple of 1000/CONFIG_HZ ms. Fixes: 857baa87b6422 ("sched/clock: Enable sched clock early") Reported-by: Gusenleitner Klaus Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: Thomas Gleixner Link: https://lore.kernel.org/20230406095735.0_14edn3@linutronix.de Link: https://lore.kernel.org/r/20230418122639.ikgfvu3f@linutronix.de --- kernel/time/tick-common.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) (limited to 'kernel/time/tick-common.c') diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c index 46789356f856..65b8658da829 100644 --- a/kernel/time/tick-common.c +++ b/kernel/time/tick-common.c @@ -218,9 +218,19 @@ 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; - tick_next_period = ktime_get(); + 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; #ifdef CONFIG_NO_HZ_FULL /* * The boot CPU may be nohz_full, in which case set -- cgit From 13bb06f8dd42071cb9a49f6e21099eea05d4b856 Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Thu, 15 Jun 2023 11:18:30 +0200 Subject: 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 Reported-by: "Bhatnagar, Rishabh" Suggested-by: Mathias Krause Signed-off-by: Thomas Gleixner Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: Thomas Gleixner Tested-by: Richard W.M. Jones Tested-by: Mathias Krause Acked-by: SeongJae Park 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(-) (limited to 'kernel/time/tick-common.c') diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c index 65b8658da829..e9138cd7a0f5 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 52254679ec48..42c0be3080bd 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); -- cgit