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rcu: Provide rcu_irq_exit_preempt() 

Interrupts and exceptions invoke rcu_irq_enter() on entry and need to
invoke rcu_irq_exit() before they either return to the interrupted code or
invoke the scheduler due to preemption.

The general assumption is that RCU idle code has to have preemption
disabled so that a return from interrupt cannot schedule. So the return
from interrupt code invokes rcu_irq_exit() and preempt_schedule_irq().

If there is any imbalance in the rcu_irq/nmi* invocations or RCU idle code
had preemption enabled then this goes unnoticed until the CPU goes idle or
some other RCU check is executed.

Provide rcu_irq_exit_preempt() which can be invoked from the
interrupt/exception return code in case that preemption is enabled. It
invokes rcu_irq_exit() and contains a few sanity checks in case that
CONFIG_PROVE_RCU is enabled to catch such issues directly.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Alexandre Chartre <alexandre.chartre@oracle.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200505134904.364456424@linutronix.de
This commit is contained in:
Thomas Gleixner 2020-05-03 15:08:52 +02:00
parent 9ea366f669
commit 8ae0ae6737
3 changed files with 24 additions and 0 deletions
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1
include/linux/rcutiny.h
View File

@ -71,6 +71,7 @@ static inline void rcu_irq_enter(void) { }
static inline void rcu_irq_exit_irqson(void) { }
static inline void rcu_irq_enter_irqson(void) { }
static inline void rcu_irq_exit(void) { }
static inline void rcu_irq_exit_preempt(void) { }
static inline void exit_rcu(void) { }
static inline bool rcu_preempt_need_deferred_qs(struct task_struct *t)
{

1
include/linux/rcutree.h
View File

@ -47,6 +47,7 @@ void rcu_idle_enter(void);
void rcu_idle_exit(void);
void rcu_irq_enter(void);
void rcu_irq_exit(void);
void rcu_irq_exit_preempt(void);
void rcu_irq_enter_irqson(void);
void rcu_irq_exit_irqson(void);

22
kernel/rcu/tree.c
View File

@ -743,6 +743,28 @@ void noinstr rcu_irq_exit(void)
rcu_nmi_exit();
}
/**
* rcu_irq_exit_preempt - Inform RCU that current CPU is exiting irq
* towards in kernel preemption
*
* Same as rcu_irq_exit() but has a sanity check that scheduling is safe
* from RCU point of view. Invoked from return from interrupt before kernel
* preemption.
*/
void rcu_irq_exit_preempt(void)
{
lockdep_assert_irqs_disabled();
rcu_nmi_exit();
RCU_LOCKDEP_WARN(__this_cpu_read(rcu_data.dynticks_nesting) <= 0,
"RCU dynticks_nesting counter underflow/zero!");
RCU_LOCKDEP_WARN(__this_cpu_read(rcu_data.dynticks_nmi_nesting) !=
DYNTICK_IRQ_NONIDLE,
"Bad RCU dynticks_nmi_nesting counter\n");
RCU_LOCKDEP_WARN(rcu_dynticks_curr_cpu_in_eqs(),
"RCU in extended quiescent state!");
}
/*
* Wrapper for rcu_irq_exit() where interrupts are enabled.
*