[PATCH 15/20] rcu/context-tracking: Move deferred nocb resched to context tracking

Frederic Weisbecker
2022-06-08T14:44:05Z

To prepare for migrating the RCU eqs accounting code to context tracking,
split the last-resort deferred nocb resched from rcu_user_enter() and
move it into a separate call from context tracking.

Acked-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@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>
---
include/linux/rcupdate.h | 6 ++++++
kernel/context_tracking.c | 8 ++++++++
kernel/rcu/tree.c | 15 ++-------------
3 files changed, 16 insertions(+), 13 deletions(-)

diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
index 910328f2f51a..1d120dca6548 100644
--- a/include/linux/rcupdate.h
+++ b/include/linux/rcupdate.h
@@ -113,6 +113,12 @@ static inline void rcu_user_enter(void) { }
static inline void rcu_user_exit(void) { }
#endif /* CONFIG_NO_HZ_FULL */

+#if defined(CONFIG_NO_HZ_FULL) && (!defined(CONFIG_GENERIC_ENTRY) || !defined(CONFIG_KVM_XFER_TO_GUEST_WORK))
+void rcu_irq_work_resched(void);
+#else
+static inline void rcu_irq_work_resched(void) { }
+#endif
+
#ifdef CONFIG_RCU_NOCB_CPU
void rcu_init_nohz(void);
int rcu_nocb_cpu_offload(int cpu);
diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c
index 95ce83904287..d782c868f36f 100644
--- a/kernel/context_tracking.c
+++ b/kernel/context_tracking.c
@@ -177,6 +177,8 @@ static __always_inline void context_tracking_recursion_exit(void)
*/
void noinstr __ct_user_enter(enum ctx_state state)
{
+ lockdep_assert_irqs_disabled();
+
/* Kernel threads aren't supposed to go to userspace */
WARN_ON_ONCE(!current->mm);

@@ -198,6 +200,12 @@ void noinstr __ct_user_enter(enum ctx_state state)
vtime_user_enter(current);
instrumentation_end();
}
+ /*
+ * Other than generic entry implementation, we may be past the last
+ * rescheduling opportunity in the entry code. Trigger a self IPI
+ * that will fire and reschedule once we resume in user/guest mode.
+ */
+ rcu_irq_work_resched();
rcu_user_enter();
}
/*
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index ef734577b63d..beddb4fb5d07 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -685,7 +685,7 @@ static DEFINE_PER_CPU(struct irq_work, late_wakeup_work) =
* last resort is to fire a local irq_work that will trigger a reschedule once IRQs
* get re-enabled again.
*/
-noinstr static void rcu_irq_work_resched(void)
+noinstr void rcu_irq_work_resched(void)
{
struct rcu_data *rdp = this_cpu_ptr(&rcu_data);

@@ -701,10 +701,7 @@ noinstr static void rcu_irq_work_resched(void)
}
instrumentation_end();
}
-
-#else
-static inline void rcu_irq_work_resched(void) { }
-#endif
+#endif /* #if !defined(CONFIG_GENERIC_ENTRY) || !defined(CONFIG_KVM_XFER_TO_GUEST_WORK) */

/**
* rcu_user_enter - inform RCU that we are resuming userspace.
@@ -719,14 +716,6 @@ static inline void rcu_irq_work_resched(void) { }
*/
noinstr void rcu_user_enter(void)
{
- lockdep_assert_irqs_disabled();
-
- /*
- * Other than generic entry implementation, we may be past the last
- * rescheduling opportunity in the entry code. Trigger a self IPI
- * that will fire and reschedule once we resume in user/guest mode.
- */
- rcu_irq_work_resched();
rcu_eqs_enter(true);
}

--
2.25.1