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https://github.com/AuxXxilium/linux_dsm_epyc7002.git
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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 */
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#ifndef LINUX_HARDIRQ_H
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#define LINUX_HARDIRQ_H
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#include <linux/context_tracking_state.h>
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#include <linux/preempt.h>
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#include <linux/lockdep.h>
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#include <linux/ftrace_irq.h>
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#include <linux/vtime.h>
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#include <asm/hardirq.h>
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extern void synchronize_irq(unsigned int irq);
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extern bool synchronize_hardirq(unsigned int irq);
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#ifdef CONFIG_NO_HZ_FULL
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void __rcu_irq_enter_check_tick(void);
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#else
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static inline void __rcu_irq_enter_check_tick(void) { }
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#endif
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static __always_inline void rcu_irq_enter_check_tick(void)
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{
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if (context_tracking_enabled())
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__rcu_irq_enter_check_tick();
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}
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/*
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* It is safe to do non-atomic ops on ->hardirq_context,
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* because NMI handlers may not preempt and the ops are
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* always balanced, so the interrupted value of ->hardirq_context
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* will always be restored.
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*/
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#define __irq_enter() \
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do { \
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account_irq_enter_time(current); \
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preempt_count_add(HARDIRQ_OFFSET); \
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lockdep_hardirq_enter(); \
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} while (0)
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/*
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* Enter irq context (on NO_HZ, update jiffies):
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*/
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extern void irq_enter(void);
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/*
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* Exit irq context without processing softirqs:
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*/
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#define __irq_exit() \
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do { \
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lockdep_hardirq_exit(); \
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account_irq_exit_time(current); \
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preempt_count_sub(HARDIRQ_OFFSET); \
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} while (0)
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/*
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* Exit irq context and process softirqs if needed:
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*/
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extern void irq_exit(void);
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#ifndef arch_nmi_enter
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#define arch_nmi_enter() do { } while (0)
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#define arch_nmi_exit() do { } while (0)
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#endif
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#ifdef CONFIG_TINY_RCU
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static inline void rcu_nmi_enter(void) { }
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static inline void rcu_nmi_exit(void) { }
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#else
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extern void rcu_nmi_enter(void);
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extern void rcu_nmi_exit(void);
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#endif
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/*
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* NMI vs Tracing
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* --------------
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*
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* We must not land in a tracer until (or after) we've changed preempt_count
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* such that in_nmi() becomes true. To that effect all NMI C entry points must
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* be marked 'notrace' and call nmi_enter() as soon as possible.
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*/
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/*
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* nmi_enter() can nest up to 15 times; see NMI_BITS.
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*/
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#define nmi_enter() \
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do { \
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arch_nmi_enter(); \
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printk_nmi_enter(); \
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lockdep_off(); \
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ftrace_nmi_enter(); \
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BUG_ON(in_nmi() == NMI_MASK); \
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__preempt_count_add(NMI_OFFSET + HARDIRQ_OFFSET); \
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rcu_nmi_enter(); \
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lockdep_hardirq_enter(); \
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} while (0)
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#define nmi_exit() \
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do { \
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lockdep_hardirq_exit(); \
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rcu_nmi_exit(); \
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BUG_ON(!in_nmi()); \
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__preempt_count_sub(NMI_OFFSET + HARDIRQ_OFFSET); \
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ftrace_nmi_exit(); \
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lockdep_on(); \
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printk_nmi_exit(); \
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arch_nmi_exit(); \
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} while (0)
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#endif /* LINUX_HARDIRQ_H */
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