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Commit 58721f5d authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: Define rcu_irq_{enter,exit}() in terms of rcu_nmi_{enter,exit}() 



RCU currently uses two different mechanisms for tracking irqs and NMIs.
This is unnecessary complexity: Given that NMIs can nest and given that
RCU's tracking handles such nesting, the NMI tracking mechanism can also
be used to track irqs.  This commit therefore defines rcu_irq_enter()
in terms of rcu_nmi_enter() and rcu_irq_exit() in terms of rcu_nmi_exit().

Unfortunately, callers must still distinguish between the irq and NMI
functions because additional actions are taken when an irq interrupts
idle or nohz_full usermode execution, and these actions cannot always
be taken from NMI handlers.

Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
parent 6136d6e4

kernel/rcu/tree.c

+21 −38
Original line number Diff line number Diff line
@@ -266,6 +266,7 @@ void rcu_bh_qs(void) 


static DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {

	.dynticks_nesting = DYNTICK_TASK_EXIT_IDLE,

	.dynticks_nmi_nesting = DYNTICK_IRQ_NONIDLE,

	.dynticks = ATOMIC_INIT(RCU_DYNTICK_CTRL_CTR),

};
@@ -914,8 +915,8 @@ void rcu_nmi_exit(void) 
 *

 * This code assumes that the idle loop never does anything that might

 * result in unbalanced calls to irq_enter() and irq_exit().  If your

 * architecture violates this assumption, RCU will give you what you

 * deserve, good and hard.  But very infrequently and irreproducibly.

 * architecture's idle loop violates this assumption, RCU will give you what

 * you deserve, good and hard.  But very infrequently and irreproducibly.

 *

 * Use things like work queues to work around this limitation.

 *
@@ -926,23 +927,14 @@ void rcu_nmi_exit(void) 
 */

void rcu_irq_exit(void)

{

	struct rcu_dynticks *rdtp;

	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);



	lockdep_assert_irqs_disabled();

	rdtp = this_cpu_ptr(&rcu_dynticks);



	/* Page faults can happen in NMI handlers, so check... */

	if (rdtp->dynticks_nmi_nesting)

		return;



	WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&

		     rdtp->dynticks_nesting < 1);

	if (rdtp->dynticks_nesting <= 1) {

		rcu_eqs_enter_common(true);

	} else {

		trace_rcu_dyntick(TPS("--="), rdtp->dynticks_nesting, rdtp->dynticks_nesting - 1);

		rdtp->dynticks_nesting--;

	}

	if (rdtp->dynticks_nmi_nesting == 1)

		rcu_prepare_for_idle();

	rcu_nmi_exit();

	if (rdtp->dynticks_nmi_nesting == 0)

		rcu_dynticks_task_enter();

}



/*
@@ -1097,12 +1089,12 @@ void rcu_nmi_enter(void) 
 * sections can occur.  The caller must have disabled interrupts.

 *

 * Note that the Linux kernel is fully capable of entering an interrupt

 * handler that it never exits, for example when doing upcalls to

 * user mode!  This code assumes that the idle loop never does upcalls to

 * user mode.  If your architecture does do upcalls from the idle loop (or

 * does anything else that results in unbalanced calls to the irq_enter()

 * and irq_exit() functions), RCU will give you what you deserve, good

 * and hard.  But very infrequently and irreproducibly.

 * handler that it never exits, for example when doing upcalls to user mode!

 * This code assumes that the idle loop never does upcalls to user mode.

 * If your architecture's idle loop does do upcalls to user mode (or does

 * anything else that results in unbalanced calls to the irq_enter() and

 * irq_exit() functions), RCU will give you what you deserve, good and hard.

 * But very infrequently and irreproducibly.

 *

 * Use things like work queues to work around this limitation.

 *
@@ -1113,23 +1105,14 @@ void rcu_nmi_enter(void) 
 */

void rcu_irq_enter(void)

{

	struct rcu_dynticks *rdtp;

	long long newval;

	struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);



	lockdep_assert_irqs_disabled();

	rdtp = this_cpu_ptr(&rcu_dynticks);



	/* Page faults can happen in NMI handlers, so check... */

	if (rdtp->dynticks_nmi_nesting)

		return;



	newval = rdtp->dynticks_nesting + 1;

	WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && newval == 0);

	if (rdtp->dynticks_nesting)

		trace_rcu_dyntick(TPS("++="), rdtp->dynticks_nesting, newval);

	else

		rcu_eqs_exit_common(newval, true);

	rdtp->dynticks_nesting++;

	if (rdtp->dynticks_nmi_nesting == 0)

		rcu_dynticks_task_exit();

	rcu_nmi_enter();

	if (rdtp->dynticks_nmi_nesting == 1)

		rcu_cleanup_after_idle();

}



/*