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authorLinus Torvalds <torvalds@linux-foundation.org>2023-06-21 12:36:34 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2023-06-21 12:36:34 -0700
commitdad9774deaf1cf8e8f7483310dfb2690310193d2 (patch)
tree0a444376047f7b664aa902f424de377e49e6e342 /kernel
parent007034977130b49b618a5206aad54f634d9f169c (diff)
parent13bb06f8dd42071cb9a49f6e21099eea05d4b856 (diff)
Merge tag 'timers-urgent-2023-06-21' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull timer fix from Thomas Gleixner: "A single regression fix for a regression fix: For a long time the tick was aligned to clock MONOTONIC so that the tick event happened at a multiple of nanoseconds per tick starting from clock MONOTONIC = 0. At some point this changed as the refined jiffies clocksource which is used during boot before the TSC or other clocksources becomes usable, was adjusted with a boot offset, so that time 0 is closer to the point where the kernel starts. This broke the assumption in the tick code that when the tick setup happens early on ktime_get() will return a multiple of nanoseconds per tick. As a consequence applications which aligned their periodic execution so that it does not collide with the tick were not longer guaranteed that the tick period starts from time 0. The fix for this regression was to realign the tick when it is initially set up to a multiple of tick periods. That works as long as the underlying tick device supports periodic mode, but breaks under certain conditions when the tick device supports only one shot mode. Depending on the offset, the alignment delta to clock MONOTONIC can get in a range where the minimal programming delta of the underlying clock event device is larger than the calculated delta to the next tick. This results in a boot hang as the tick code tries to play catch up, but as the tick never fires jiffies are not advanced so it keeps trying for ever. Solve this by moving the tick alignement into the NOHZ / HIGHRES enablement code because at that point it is guaranteed that the underlying clocksource is high resolution capable and not longer depending on the tick. This is far before user space starts, so at the point where applications try to align their timers, the old behaviour of the tick happening at a multiple of nanoseconds per tick starting from clock MONOTONIC = 0 is restored" * tag 'timers-urgent-2023-06-21' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: tick/common: Align tick period during sched_timer setup
Diffstat (limited to 'kernel')
-rw-r--r--kernel/time/tick-common.c13
-rw-r--r--kernel/time/tick-sched.c13
2 files changed, 13 insertions, 13 deletions
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);