aaf2bc50df
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
110 lines
2.6 KiB
C
110 lines
2.6 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
|
|
#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);
|
|
|
|
#ifdef CONFIG_NO_HZ_FULL
|
|
void __rcu_irq_enter_check_tick(void);
|
|
#else
|
|
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
|
|
* always balanced, so the interrupted value of ->hardirq_context
|
|
* will always be restored.
|
|
*/
|
|
#define __irq_enter() \
|
|
do { \
|
|
account_irq_enter_time(current); \
|
|
preempt_count_add(HARDIRQ_OFFSET); \
|
|
lockdep_hardirq_enter(); \
|
|
} while (0)
|
|
|
|
/*
|
|
* Enter irq context (on NO_HZ, update jiffies):
|
|
*/
|
|
extern void irq_enter(void);
|
|
|
|
/*
|
|
* Exit irq context without processing softirqs:
|
|
*/
|
|
#define __irq_exit() \
|
|
do { \
|
|
lockdep_hardirq_exit(); \
|
|
account_irq_exit_time(current); \
|
|
preempt_count_sub(HARDIRQ_OFFSET); \
|
|
} while (0)
|
|
|
|
/*
|
|
* Exit irq context and process softirqs if needed:
|
|
*/
|
|
extern void irq_exit(void);
|
|
|
|
#ifndef arch_nmi_enter
|
|
#define arch_nmi_enter() do { } while (0)
|
|
#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
|
|
* --------------
|
|
*
|
|
* We must not land in a tracer until (or after) we've changed preempt_count
|
|
* such that in_nmi() becomes true. To that effect all NMI C entry points must
|
|
* be marked 'notrace' and call nmi_enter() as soon as possible.
|
|
*/
|
|
|
|
/*
|
|
* nmi_enter() can nest up to 15 times; see NMI_BITS.
|
|
*/
|
|
#define nmi_enter() \
|
|
do { \
|
|
arch_nmi_enter(); \
|
|
printk_nmi_enter(); \
|
|
lockdep_off(); \
|
|
ftrace_nmi_enter(); \
|
|
BUG_ON(in_nmi() == NMI_MASK); \
|
|
__preempt_count_add(NMI_OFFSET + HARDIRQ_OFFSET); \
|
|
rcu_nmi_enter(); \
|
|
lockdep_hardirq_enter(); \
|
|
} while (0)
|
|
|
|
#define nmi_exit() \
|
|
do { \
|
|
lockdep_hardirq_exit(); \
|
|
rcu_nmi_exit(); \
|
|
BUG_ON(!in_nmi()); \
|
|
__preempt_count_sub(NMI_OFFSET + HARDIRQ_OFFSET); \
|
|
ftrace_nmi_exit(); \
|
|
lockdep_on(); \
|
|
printk_nmi_exit(); \
|
|
arch_nmi_exit(); \
|
|
} while (0)
|
|
|
|
#endif /* LINUX_HARDIRQ_H */
|