rcu: Clamp ->dynticks_nmi_nesting at eqs entry/exit (6136d6e4) · Commits · 戴 / test

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>

kernel/rcu/rcu.h

+2 −0

Original line number	Diff line number	Diff line
		@@ -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.

kernel/rcu/tree.c

+2 −0

Original line number	Diff line number	Diff line
		@@ -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);
		}
		}

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