linux-kernel - [PATCH 17/21] rcu/context-tracking: Move deferred nocb resched to context tracking

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Message-Id: <20220503100051.2799723-18-frederic@kernel.org>
Date:   Tue,  3 May 2022 12:00:47 +0200
From:   Frederic Weisbecker <frederic@...nel.org>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Frederic Weisbecker <frederic@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Phil Auld <pauld@...hat.com>,
        Alex Belits <abelits@...vell.com>,
        Nicolas Saenz Julienne <nsaenz@...nel.org>,
        Xiongfeng Wang <wangxiongfeng2@...wei.com>,
        Neeraj Upadhyay <quic_neeraju@...cinc.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Yu Liao <liaoyu15@...wei.com>,
        Boqun Feng <boqun.feng@...il.com>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Marcelo Tosatti <mtosatti@...hat.com>,
        Paul Gortmaker <paul.gortmaker@...driver.com>,
        Uladzislau Rezki <uladzislau.rezki@...y.com>,
        Joel Fernandes <joel@...lfernandes.org>
Subject: [PATCH 17/21] rcu/context-tracking: Move deferred nocb resched to context tracking

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@...nel.org>
Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Neeraj Upadhyay <quic_neeraju@...cinc.com>
Cc: Uladzislau Rezki <uladzislau.rezki@...y.com>
Cc: Joel Fernandes <joel@...lfernandes.org>
Cc: Boqun Feng <boqun.feng@...il.com>
Cc: Nicolas Saenz Julienne <nsaenz@...nel.org>
Cc: Marcelo Tosatti <mtosatti@...hat.com>
Cc: Xiongfeng Wang <wangxiongfeng2@...wei.com>
Cc: Yu Liao<liaoyu15@...wei.com>
Cc: Phil Auld <pauld@...hat.com>
Cc: Paul Gortmaker<paul.gortmaker@...driver.com>
Cc: Alex Belits <abelits@...vell.com>
---
 include/linux/rcutree.h   |  6 ++++++
 kernel/context_tracking.c |  8 ++++++++
 kernel/rcu/tree.c         | 15 ++-------------
 3 files changed, 16 insertions(+), 13 deletions(-)

diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
index cafe3fbf4272..6294271f1615 100644
--- a/include/linux/rcutree.h
+++ b/include/linux/rcutree.h
@@ -76,4 +76,10 @@ int rcutree_dead_cpu(unsigned int cpu);
 int rcutree_dying_cpu(unsigned int cpu);
 void rcu_cpu_starting(unsigned int cpu);
 
+#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
+
 #endif /* __LINUX_RCUTREE_H */
diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c
index 14f04c521573..4ca4aeadad06 100644
--- a/kernel/context_tracking.c
+++ b/kernel/context_tracking.c
@@ -60,6 +60,8 @@ 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);
 
@@ -81,6 +83,12 @@ 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 7b1404db3c17..7d1a3e73ff25 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -681,7 +681,7 @@ 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);
 
@@ -697,10 +697,7 @@ 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.
@@ -715,14 +712,6 @@ 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