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rcutorture: Also force sched priority to timersd on boosting test.

Browse Source 
BugLink: https://bugs.launchpad.net/bugs/2060704

ksoftirqd is statically boosted to the priority level right above the
one of rcu_torture_boost() so that timers, which torture readers rely on,
get a chance to run while rcu_torture_boost() is polling.

However timers processing got split from ksoftirqd into their own kthread
(timersd) that isn't boosted. It has the same SCHED_FIFO low prio as
rcu_torture_boost() and therefore timers can't preempt it and may
starve.

The issue can be triggered in practice on v5.17.1-rt17 using:

	./kvm.sh --allcpus --configs TREE04 --duration 10m --kconfig "CONFIG_EXPERT=y CONFIG_PREEMPT_RT=y"

Fix this with statically boosting timersd just like is done with
ksoftirqd in commit
   ea6d962e80 ("rcutorture: Judge RCU priority boosting on grace periods, not callbacks")

Suggested-by: Mel Gorman <mgorman@suse.de>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lkml.kernel.org/r/20220405010752.1347437-1-frederic@kernel.org
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Kevin Becker <kevin.becker@canonical.com>
This commit is contained in:
Frederic Weisbecker
2022-04-05 03:07:51 +02:00
committed by Kevin Becker
parent 98c07e4349
commit a54fb070e1
3 changed files with 8 additions and 1 deletions
Download Patch File Download Diff File Expand all files Collapse all files
include/linux/interrupt.h
+1
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@@ -613,6 +613,7 @@ extern void raise_softirq_irqoff(unsigned int nr);
extern void raise_softirq(unsigned int nr);
#ifdef CONFIG_PREEMPT_RT
DECLARE_PER_CPU(struct task_struct *, timersd);
extern void raise_timer_softirq(void);
extern void raise_hrtimer_softirq(void);
kernel/rcu/rcutorture.c
+6
View File
@@ -2410,6 +2410,12 @@ static int rcutorture_booster_init(unsigned int cpu)
WARN_ON_ONCE(!t);
sp.sched_priority = 2;
sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
#ifdef CONFIG_PREEMPT_RT
t = per_cpu(timersd, cpu);
WARN_ON_ONCE(!t);
sp.sched_priority = 2;
sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
#endif
}
/* Don't allow time recalculation while creating a new task. */
kernel/softirq.c
+1 -1
View File
@@ -631,7 +631,7 @@ static inline void tick_irq_exit(void)
}
#ifdef CONFIG_PREEMPT_RT
static DEFINE_PER_CPU(struct task_struct *, timersd);
DEFINE_PER_CPU(struct task_struct *, timersd);
static DEFINE_PER_CPU(unsigned long, pending_timer_softirq);
static unsigned int local_pending_timers(void)