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rcu: Clamp ->dynticks_nmi_nesting at eqs entry/exit

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In preparation for merging dyntick-idle irq handling into the NMI
algorithm, clamp ->dynticks_nmi_nesting value to allow for interrupts
that enter but never leave and vice versa.

It is important that the clamping happen outside of the extended quiescent
state.  Otherwise, there will be short windows where irqs and NMIs fail
to convince RCU to start watching.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney 2017-10-03 08:28:04 -07:00
parent fd581a91ac
commit 6136d6e48a
2 changed files with 4 additions and 0 deletions
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2
kernel/rcu/rcu.h
View File

@ -56,6 +56,8 @@
#define DYNTICK_TASK_EXIT_IDLE (DYNTICK_TASK_NEST_VALUE + \
DYNTICK_TASK_FLAG)
#define DYNTICK_IRQ_NONIDLE ((INT_MAX / 2) + 1)
/*
* Grace-period counter management.

2
kernel/rcu/tree.c
View File

@ -818,6 +818,7 @@ static void rcu_eqs_enter(bool user)
struct rcu_dynticks *rdtp;
rdtp = this_cpu_ptr(&rcu_dynticks);
WRITE_ONCE(rdtp->dynticks_nmi_nesting, 0);
WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
(rdtp->dynticks_nesting & DYNTICK_TASK_NEST_MASK) == 0);
if ((rdtp->dynticks_nesting & DYNTICK_TASK_NEST_MASK) == DYNTICK_TASK_NEST_VALUE)
@ -1008,6 +1009,7 @@ static void rcu_eqs_exit(bool user)
rcu_eqs_exit_common(DYNTICK_TASK_EXIT_IDLE, user);
rdtp->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
__this_cpu_dec(disable_rcu_irq_enter);
WRITE_ONCE(rdtp->dynticks_nmi_nesting, DYNTICK_IRQ_NONIDLE);
}
}