[PATCH v3 05/22] rcu: Make RCU IRQ enter/exit functions rely on in_nmi()

Peter Zijlstra
2020-02-19T15:14:34Z

From: Paul E. McKenney <paulmck@kernel.org>

The rcu_nmi_enter_common() and rcu_nmi_exit_common() functions take an
"irq" parameter that indicates whether these functions are invoked from
an irq handler (irq==true) or an NMI handler (irq==false). However,
recent changes have applied notrace to a few critical functions such
that rcu_nmi_enter_common() and rcu_nmi_exit_common() many now rely
on in_nmi(). Note that in_nmi() works no differently than before,
but rather that tracing is now prohibited in code regions where in_nmi()
would incorrectly report NMI state.

This commit therefore removes the "irq" parameter and inlines
rcu_nmi_enter_common() and rcu_nmi_exit_common() into rcu_nmi_enter()
and rcu_nmi_exit(), respectively.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
kernel/rcu/tree.c | 45 ++++++++++++++-------------------------------
1 file changed, 14 insertions(+), 31 deletions(-)

--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -614,16 +614,18 @@ void rcu_user_enter(void)
}
#endif /* CONFIG_NO_HZ_FULL */

-/*
+/**
+ * rcu_nmi_exit - inform RCU of exit from NMI context
+ *
* If we are returning from the outermost NMI handler that interrupted an
* RCU-idle period, update rdp->dynticks and rdp->dynticks_nmi_nesting
* to let the RCU grace-period handling know that the CPU is back to
* being RCU-idle.
*
- * If you add or remove a call to rcu_nmi_exit_common(), be sure to test
+ * If you add or remove a call to rcu_nmi_exit(), be sure to test
* with CONFIG_RCU_EQS_DEBUG=y.
*/
-static __always_inline void rcu_nmi_exit_common(bool irq)
+void rcu_nmi_exit(void)
{
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);

@@ -651,27 +653,16 @@ static __always_inline void rcu_nmi_exit
trace_rcu_dyntick(TPS("Startirq"), rdp->dynticks_nmi_nesting, 0, atomic_read(&rdp->dynticks));
WRITE_ONCE(rdp->dynticks_nmi_nesting, 0); /* Avoid store tearing. */

- if (irq)
+ if (!in_nmi())
rcu_prepare_for_idle();

rcu_dynticks_eqs_enter();

- if (irq)
+ if (!in_nmi())
rcu_dynticks_task_enter();
}

/**
- * rcu_nmi_exit - inform RCU of exit from NMI context
- *
- * If you add or remove a call to rcu_nmi_exit(), be sure to test
- * with CONFIG_RCU_EQS_DEBUG=y.
- */
-void rcu_nmi_exit(void)
-{
- rcu_nmi_exit_common(false);
-}
-
-/**
* rcu_irq_exit - inform RCU that current CPU is exiting irq towards idle
*
* Exit from an interrupt handler, which might possibly result in entering
@@ -693,7 +684,7 @@ void rcu_nmi_exit(void)
void rcu_irq_exit(void)
{
lockdep_assert_irqs_disabled();
- rcu_nmi_exit_common(true);
+ rcu_nmi_exit();
}

/*
@@ -777,7 +768,7 @@ void rcu_user_exit(void)
#endif /* CONFIG_NO_HZ_FULL */

/**
- * rcu_nmi_enter_common - inform RCU of entry to NMI context
+ * rcu_nmi_enter - inform RCU of entry to NMI context
* @irq: Is this call from rcu_irq_enter?
*
* If the CPU was idle from RCU's viewpoint, update rdp->dynticks and
@@ -786,10 +777,10 @@ void rcu_user_exit(void)
* long as the nesting level does not overflow an int. (You will probably
* run out of stack space first.)
*
- * If you add or remove a call to rcu_nmi_enter_common(), be sure to test
+ * If you add or remove a call to rcu_nmi_enter(), be sure to test
* with CONFIG_RCU_EQS_DEBUG=y.
*/
-static __always_inline void rcu_nmi_enter_common(bool irq)
+void rcu_nmi_enter(void)
{
long incby = 2;
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
@@ -807,12 +798,12 @@ static __always_inline void rcu_nmi_ente
*/
if (rcu_dynticks_curr_cpu_in_eqs()) {

- if (irq)
+ if (!in_nmi())
rcu_dynticks_task_exit();

rcu_dynticks_eqs_exit();

- if (irq)
+ if (!in_nmi())
rcu_cleanup_after_idle();

incby = 1;
@@ -834,14 +825,6 @@ static __always_inline void rcu_nmi_ente
rdp->dynticks_nmi_nesting + incby);
barrier();
}
-
-/**
- * rcu_nmi_enter - inform RCU of entry to NMI context
- */
-void rcu_nmi_enter(void)
-{
- rcu_nmi_enter_common(false);
-}
NOKPROBE_SYMBOL(rcu_nmi_enter);

/**
@@ -869,7 +852,7 @@ NOKPROBE_SYMBOL(rcu_nmi_enter);
void rcu_irq_enter(void)
{
lockdep_assert_irqs_disabled();
- rcu_nmi_enter_common(true);
+ rcu_nmi_enter();
}

/*