[PATCH 19/21] rcu/context-tracking: Remove unused and/or unecessary middle functions

Frederic Weisbecker
2022-05-03T10:03:06Z

Some eqs functions are now only used internally by context tracking, so
their public declarations can be removed.

Also middle functions such as rcu_user_*() and rcu_idle_*()
which now directly call to rcu_eqs_enter() and rcu_eqs_exit() can be
wiped out as well.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Paul E. McKenney <paulmck@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Neeraj Upadhyay <quic_neeraju@quicinc.com>
Cc: Uladzislau Rezki <uladzislau.rezki@sony.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Nicolas Saenz Julienne <nsaenz@kernel.org>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Xiongfeng Wang <wangxiongfeng2@huawei.com>
Cc: Yu Liao<liaoyu15@huawei.com>
Cc: Phil Auld <pauld@redhat.com>
Cc: Paul Gortmaker<paul.gortmaker@windriver.com>
Cc: Alex Belits <abelits@marvell.com>
---
Documentation/RCU/stallwarn.rst | 2 +-
include/linux/hardirq.h | 8 --
include/linux/rcupdate.h | 8 --
include/linux/rcutiny.h | 2 -
include/linux/rcutree.h | 2 -
kernel/context_tracking.c | 147 +++++++++++---------------------
6 files changed, 50 insertions(+), 119 deletions(-)

diff --git a/Documentation/RCU/stallwarn.rst b/Documentation/RCU/stallwarn.rst
index 7858c3afa1f4..bebcaef475a6 100644
--- a/Documentation/RCU/stallwarn.rst
+++ b/Documentation/RCU/stallwarn.rst
@@ -97,7 +97,7 @@ warnings:
which will include additional debugging information.

- A low-level kernel issue that either fails to invoke one of the
- variants of rcu_user_enter(), rcu_user_exit(), ct_idle_enter(),
+ variants of rcu_eqs_enter(true), rcu_eqs_exit(true), ct_idle_enter(),
ct_idle_exit(), ct_irq_enter(), or ct_irq_exit() on the one
hand, or that invokes one of them too many times on the other.
Historically, the most frequent issue has been an omission
diff --git a/include/linux/hardirq.h b/include/linux/hardirq.h
index 345cdbe9c1b7..d57cab4d4c06 100644
--- a/include/linux/hardirq.h
+++ b/include/linux/hardirq.h
@@ -92,14 +92,6 @@ void irq_exit_rcu(void);
#define arch_nmi_exit() do { } while (0)
#endif

-#ifdef CONFIG_TINY_RCU
-static inline void rcu_nmi_enter(void) { }
-static inline void rcu_nmi_exit(void) { }
-#else
-extern void rcu_nmi_enter(void);
-extern void rcu_nmi_exit(void);
-#endif
-
/*
* NMI vs Tracing
* --------------
diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 923e4fa04338..79ea1a45adf0 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -105,14 +105,6 @@ static inline void rcu_sysrq_start(void) { }
static inline void rcu_sysrq_end(void) { }
#endif /* #else #ifdef CONFIG_RCU_STALL_COMMON */

-#ifdef CONFIG_NO_HZ_FULL
-void rcu_user_enter(void);
-void rcu_user_exit(void);
-#else
-static inline void rcu_user_enter(void) { }
-static inline void rcu_user_exit(void) { }
-#endif /* CONFIG_NO_HZ_FULL */
-
#ifdef CONFIG_RCU_NOCB_CPU
void rcu_init_nohz(void);
int rcu_nocb_cpu_offload(int cpu);
diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
index 5921d9ae7ab5..430aac8a7344 100644
--- a/include/linux/rcutiny.h
+++ b/include/linux/rcutiny.h
@@ -86,8 +86,6 @@ static inline int rcu_needs_cpu(void)
static inline void rcu_virt_note_context_switch(int cpu) { }
static inline void rcu_cpu_stall_reset(void) { }
static inline int rcu_jiffies_till_stall_check(void) { return 21 * HZ; }
-static inline void rcu_idle_enter(void) { }
-static inline void rcu_idle_exit(void) { }
static inline void rcu_irq_exit_check_preempt(void) { }
#define rcu_is_idle_cpu(cpu) \
(is_idle_task(current) && !in_nmi() && !in_hardirq() && !in_serving_softirq())
diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
index d9e8e6233c47..72131447762e 100644
--- a/include/linux/rcutree.h
+++ b/include/linux/rcutree.h
@@ -47,8 +47,6 @@ unsigned long start_poll_synchronize_rcu(void);
bool poll_state_synchronize_rcu(unsigned long oldstate);
void cond_synchronize_rcu(unsigned long oldstate);

-void rcu_idle_enter(void);
-void rcu_idle_exit(void);
bool rcu_is_idle_cpu(int cpu);

#ifdef CONFIG_PROVE_RCU
diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c
index 279fb5875dd8..b906fb55903b 100644
--- a/kernel/context_tracking.c
+++ b/kernel/context_tracking.c
@@ -140,52 +140,17 @@ static noinstr void rcu_eqs_enter(bool user)
}

/**
- * rcu_idle_enter - inform RCU that current CPU is entering idle
- *
- * Enter idle mode, in other words, -leave- the mode in which RCU
- * read-side critical sections can occur. (Though RCU read-side
- * critical sections can occur in irq handlers in idle, a possibility
- * handled by irq_enter() and irq_exit().)
- *
- * If you add or remove a call to rcu_idle_enter(), be sure to test with
- * CONFIG_RCU_EQS_DEBUG=y.
- */
-noinstr void rcu_idle_enter(void)
-{
- lockdep_assert_irqs_disabled();
- rcu_eqs_enter(false);
-}
-
-#ifdef CONFIG_NO_HZ_FULL
-/**
- * rcu_user_enter - inform RCU that we are resuming userspace.
- *
- * Enter RCU idle mode right before resuming userspace. No use of RCU
- * is permitted between this call and rcu_user_exit(). This way the
- * CPU doesn't need to maintain the tick for RCU maintenance purposes
- * when the CPU runs in userspace.
- *
- * If you add or remove a call to rcu_user_enter(), be sure to test with
- * CONFIG_RCU_EQS_DEBUG=y.
- */
-noinstr void rcu_user_enter(void)
-{
- rcu_eqs_enter(true);
-}
-#endif /* CONFIG_NO_HZ_FULL */
-
-/**
- * rcu_nmi_exit - inform RCU of exit from NMI context
+ * ct_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 ct->dynticks and ct->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(), be sure to test
+ * If you add or remove a call to ct_nmi_exit(), be sure to test
* with CONFIG_RCU_EQS_DEBUG=y.
*/
-noinstr void rcu_nmi_exit(void)
+noinstr void ct_nmi_exit(void)
{
struct context_tracking *ct = this_cpu_ptr(&context_tracking);

@@ -266,46 +231,7 @@ static void noinstr rcu_eqs_exit(bool user)
}

/**
- * rcu_idle_exit - inform RCU that current CPU is leaving idle
- *
- * Exit idle mode, in other words, -enter- the mode in which RCU
- * read-side critical sections can occur.
- *
- * If you add or remove a call to rcu_idle_exit(), be sure to test with
- * CONFIG_RCU_EQS_DEBUG=y.
- *
- * FIXME: This function should be noinstr but the below local_irq_save() is
- * unsafe because it involves illegal RCU uses through tracing and lockdep.
- * This must be fixed first.
- */
-void rcu_idle_exit(void)
-{
- unsigned long flags;
-
- local_irq_save(flags);
- rcu_eqs_exit(false);
- local_irq_restore(flags);
-}
-EXPORT_SYMBOL_GPL(rcu_idle_exit);
-
-#ifdef CONFIG_NO_HZ_FULL
-/**
- * rcu_user_exit - inform RCU that we are exiting userspace.
- *
- * Exit RCU idle mode while entering the kernel because it can
- * run a RCU read side critical section anytime.
- *
- * If you add or remove a call to rcu_user_exit(), be sure to test with
- * CONFIG_RCU_EQS_DEBUG=y.
- */
-void noinstr rcu_user_exit(void)
-{
- rcu_eqs_exit(true);
-}
-#endif /* ifdef CONFIG_NO_HZ_FULL */
-
-/**
- * rcu_nmi_enter - inform RCU of entry to NMI context
+ * ct_nmi_enter - inform RCU of entry to NMI context
*
* If the CPU was idle from RCU's viewpoint, update ct->dynticks and
* ct->dynticks_nmi_nesting to let the RCU grace-period handling know
@@ -313,10 +239,10 @@ void noinstr 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(), be sure to test
+ * If you add or remove a call to ct_nmi_enter(), be sure to test
* with CONFIG_RCU_EQS_DEBUG=y.
*/
-noinstr void rcu_nmi_enter(void)
+noinstr void ct_nmi_enter(void)
{
long incby = 2;
struct context_tracking *ct = this_cpu_ptr(&context_tracking);
@@ -431,7 +357,13 @@ void noinstr __ct_user_enter(enum ctx_state state)
* that will fire and reschedule once we resume in user/guest mode.
*/
rcu_irq_work_resched();
- rcu_user_enter();
+ /*
+ * Enter RCU idle mode right before resuming userspace. No use of RCU
+ * is permitted between this call and rcu_eqs_exit(). This way the
+ * CPU doesn't need to maintain the tick for RCU maintenance purposes
+ * when the CPU runs in userspace.
+ */
+ rcu_eqs_enter(true);
}
/*
* Even if context tracking is disabled on this CPU, because it's outside
@@ -464,7 +396,7 @@ void ct_user_enter(enum ctx_state state)
/*
* Some contexts may involve an exception occuring in an irq,
* leading to that nesting:
- * ct_irq_enter() rcu_user_exit() rcu_user_exit() ct_irq_exit()
+ * ct_irq_enter() rcu_eqs_exit(true) rcu_eqs_enter(true) ct_irq_exit()
* This would mess up the dyntick_nesting count though. And rcu_irq_*()
* helpers are enough to protect RCU uses inside the exception. So
* just return immediately if we detect we are in an IRQ.
@@ -513,10 +445,10 @@ void noinstr __ct_user_exit(enum ctx_state state)
if (__this_cpu_read(context_tracking.state) == state) {
if (__this_cpu_read(context_tracking.active)) {
/*
- * We are going to run code that may use RCU. Inform
- * RCU core about that (ie: we may need the tick again).
+ * Exit RCU idle mode while entering the kernel because it can
+ * run a RCU read side critical section anytime.
*/
- rcu_user_exit();
+ rcu_eqs_exit(true);
if (state == CONTEXT_USER) {
instrumentation_begin();
vtime_user_exit(current);
@@ -606,16 +538,45 @@ DEFINE_PER_CPU(struct context_tracking, context_tracking) = {
};
EXPORT_SYMBOL_GPL(context_tracking);

-
+/**
+ * ct_idle_enter - inform RCU that current CPU is entering idle
+ *
+ * Enter idle mode, in other words, -leave- the mode in which RCU
+ * read-side critical sections can occur. (Though RCU read-side
+ * critical sections can occur in irq handlers in idle, a possibility
+ * handled by irq_enter() and irq_exit().)
+ *
+ * If you add or remove a call to ct_idle_enter(), be sure to test with
+ * CONFIG_RCU_EQS_DEBUG=y.
+ */
noinstr void ct_idle_enter(void)
{
- rcu_idle_enter();
+ lockdep_assert_irqs_disabled();
+ rcu_eqs_enter(false);
}
EXPORT_SYMBOL_GPL(ct_idle_enter);

+/**
+ * ct_idle_exit - inform RCU that current CPU is leaving idle
+ *
+ * Exit idle mode, in other words, -enter- the mode in which RCU
+ * read-side critical sections can occur.
+ *
+ * If you add or remove a call to ct_idle_exit(), be sure to test with
+ * CONFIG_RCU_EQS_DEBUG=y.
+ *
+ * FIXME: This function should be noinstr but the below local_irq_save() is
+ * unsafe because it involves illegal RCU uses through tracing and lockdep.
+ * This must be fixed first.
+ */
void ct_idle_exit(void)
{
- rcu_idle_exit();
+ unsigned long flags;
+
+ local_irq_save(flags);
+ rcu_eqs_exit(false);
+ local_irq_restore(flags);
+
}
EXPORT_SYMBOL_GPL(ct_idle_exit);

@@ -709,13 +670,3 @@ void ct_irq_exit_irqson(void)
ct_irq_exit();
local_irq_restore(flags);
}
-
-noinstr void ct_nmi_enter(void)
-{
- rcu_nmi_enter();
-}
-
-noinstr void ct_nmi_exit(void)
-{
- rcu_nmi_exit();
-}
--
2.25.1