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rcu: Abstract out rcu_irq_enter_check_tick() from rcu_nmi_enter()

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There will likely be exception handlers that can sleep, which rules
out the usual approach of invoking rcu_nmi_enter() on entry and also
rcu_nmi_exit() on all exit paths.  However, the alternative approach of
just not calling anything can prevent RCU from coaxing quiescent states
from nohz_full CPUs that are looping in the kernel:  RCU must instead
IPI them explicitly.  It would be better to enable the scheduler tick
on such CPUs to interact with RCU in a lighter-weight manner, and this
enabling is one of the things that rcu_nmi_enter() currently does.

What is needed is something that helps RCU coax quiescent states while
not preventing subsequent sleeps.  This commit therefore splits out the
nohz_full scheduler-tick enabling from the rest of the rcu_nmi_enter()
logic into a new function named rcu_irq_enter_check_tick().

[ tglx: Renamed the function and made it a nop when context tracking is off ]
[ mingo: Fixed a CONFIG_NO_HZ_FULL assumption, harmonized and fixed all the
         comment blocks and cleaned up rcu_nmi_enter()/exit() definitions. ]

Suggested-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20200521202116.996113173@linutronix.de
This commit is contained in:
Paul E. McKenney 2020-05-21 22:05:15 +02:00 • committed by Ingo Molnar
parent b1fcf9b83c
commit aaf2bc50df
2 changed files with 80 additions and 33 deletions
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31
include/linux/hardirq.h
View file

@ -2,31 +2,28 @@
#ifndef LINUX_HARDIRQ_H
#define LINUX_HARDIRQ_H
#include <linux/context_tracking_state.h>
#include <linux/preempt.h>
#include <linux/lockdep.h>
#include <linux/ftrace_irq.h>
#include <linux/vtime.h>
#include <asm/hardirq.h>
extern void synchronize_irq(unsigned int irq);
extern bool synchronize_hardirq(unsigned int irq);
#if defined(CONFIG_TINY_RCU)
static inline void rcu_nmi_enter(void)
{
}
static inline void rcu_nmi_exit(void)
{
}
#ifdef CONFIG_NO_HZ_FULL
void __rcu_irq_enter_check_tick(void);
#else
extern void rcu_nmi_enter(void);
extern void rcu_nmi_exit(void);
static inline void __rcu_irq_enter_check_tick(void) { }
#endif
static __always_inline void rcu_irq_enter_check_tick(void)
{
if (context_tracking_enabled())
__rcu_irq_enter_check_tick();
}
/*
* It is safe to do non-atomic ops on ->hardirq_context,
* because NMI handlers may not preempt and the ops are
@ -65,6 +62,14 @@ extern void irq_exit(void);
#define arch_nmi_exit() do { } while (0)
#endif
#ifdef CONFIG_TINY_RCU
static inline void rcu_nmi_enter(void) { }
static inline void rcu_nmi_exit(void) { }
#else
extern void rcu_nmi_enter(void);
extern void rcu_nmi_exit(void);
#endif
/*
* NMI vs Tracing
* --------------