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Diffstat (limited to '')
| -rw-r--r-- | debian/patches-rt/0014-tick-Fix-timer-storm-since-introduction-of-timersd.patch | 116 |
1 files changed, 116 insertions, 0 deletions
diff --git a/debian/patches-rt/0014-tick-Fix-timer-storm-since-introduction-of-timersd.patch b/debian/patches-rt/0014-tick-Fix-timer-storm-since-introduction-of-timersd.patch new file mode 100644 index 000000000..11eeed939 --- /dev/null +++ b/debian/patches-rt/0014-tick-Fix-timer-storm-since-introduction-of-timersd.patch @@ -0,0 +1,116 @@ +From ae3e63c4320c0c2d3865ba8ecff64a6d03948ce7 Mon Sep 17 00:00:00 2001 +From: Frederic Weisbecker <frederic@kernel.org> +Date: Tue, 5 Apr 2022 03:07:52 +0200 +Subject: [PATCH 14/62] tick: Fix timer storm since introduction of timersd +Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.1/older/patches-6.1.69-rt21.tar.xz + +If timers are pending while the tick is reprogrammed on nohz_mode, the +next expiry is not armed to fire now, it is delayed one jiffy forward +instead so as not to raise an inextinguishable timer storm with such +scenario: + +1) IRQ triggers and queue a timer +2) ksoftirqd() is woken up +3) IRQ tail: timer is reprogrammed to fire now +4) IRQ exit +5) TIMER interrupt +6) goto 3) + +...all that until we finally reach ksoftirqd. + +Unfortunately we are checking the wrong softirq vector bitmask since +timersd kthread has split from ksoftirqd. Timers now have their own +vector state field that must be checked separately. As a result, the +old timer storm is back. This shows up early on boot with extremely long +initcalls: + + [ 333.004807] initcall dquot_init+0x0/0x111 returned 0 after 323822879 usecs + +and the cause is uncovered with the right trace events showing just +10 microseconds between ticks (~100 000 Hz): + +|swapper/-1 1dn.h111 60818582us : hrtimer_expire_entry: hrtimer=00000000e0ef0f6b function=tick_sched_timer now=60415486608 +|swapper/-1 1dn.h111 60818592us : hrtimer_expire_entry: hrtimer=00000000e0ef0f6b function=tick_sched_timer now=60415496082 +|swapper/-1 1dn.h111 60818601us : hrtimer_expire_entry: hrtimer=00000000e0ef0f6b function=tick_sched_timer now=60415505550 + +Fix this by checking the right timer vector state from the nohz code. + +Signed-off-by: Frederic Weisbecker <frederic@kernel.org> +Cc: Mel Gorman <mgorman@suse.de> +Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de> +Cc: Thomas Gleixner <tglx@linutronix.de> +Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> +Link: https://lkml.kernel.org/r/20220405010752.1347437-2-frederic@kernel.org +--- + include/linux/interrupt.h | 12 ++++++++++++ + kernel/softirq.c | 7 +------ + kernel/time/tick-sched.c | 2 +- + 3 files changed, 14 insertions(+), 7 deletions(-) + +diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h +index f459b0f27c94..a5091ac97fc6 100644 +--- a/include/linux/interrupt.h ++++ b/include/linux/interrupt.h +@@ -611,9 +611,16 @@ extern void raise_softirq(unsigned int nr); + + #ifdef CONFIG_PREEMPT_RT + DECLARE_PER_CPU(struct task_struct *, timersd); ++DECLARE_PER_CPU(unsigned long, pending_timer_softirq); ++ + extern void raise_timer_softirq(void); + extern void raise_hrtimer_softirq(void); + ++static inline unsigned int local_pending_timers(void) ++{ ++ return __this_cpu_read(pending_timer_softirq); ++} ++ + #else + static inline void raise_timer_softirq(void) + { +@@ -624,6 +631,11 @@ static inline void raise_hrtimer_softirq(void) + { + raise_softirq_irqoff(HRTIMER_SOFTIRQ); + } ++ ++static inline unsigned int local_pending_timers(void) ++{ ++ return local_softirq_pending(); ++} + #endif + + DECLARE_PER_CPU(struct task_struct *, ksoftirqd); +diff --git a/kernel/softirq.c b/kernel/softirq.c +index 1892af494cdd..ab1fe34326ba 100644 +--- a/kernel/softirq.c ++++ b/kernel/softirq.c +@@ -639,12 +639,7 @@ static inline void tick_irq_exit(void) + + #ifdef CONFIG_PREEMPT_RT + DEFINE_PER_CPU(struct task_struct *, timersd); +-static DEFINE_PER_CPU(unsigned long, pending_timer_softirq); +- +-static unsigned int local_pending_timers(void) +-{ +- return __this_cpu_read(pending_timer_softirq); +-} ++DEFINE_PER_CPU(unsigned long, pending_timer_softirq); + + static void wake_timersd(void) + { +diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c +index 798e1841d286..b52e1861b913 100644 +--- a/kernel/time/tick-sched.c ++++ b/kernel/time/tick-sched.c +@@ -800,7 +800,7 @@ static void tick_nohz_restart(struct tick_sched *ts, ktime_t now) + + static inline bool local_timer_softirq_pending(void) + { +- return local_softirq_pending() & BIT(TIMER_SOFTIRQ); ++ return local_pending_timers() & BIT(TIMER_SOFTIRQ); + } + + static ktime_t tick_nohz_next_event(struct tick_sched *ts, int cpu) +-- +2.43.0 + |