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 <[email protected]>
Signed-off-by: Frederic Weisbecker <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Neeraj Upadhyay <[email protected]>
Cc: Uladzislau Rezki <[email protected]>
Cc: Joel Fernandes <[email protected]>
Cc: Boqun Feng <[email protected]>
Cc: Nicolas Saenz Julienne <[email protected]>
Cc: Marcelo Tosatti <[email protected]>
Cc: Xiongfeng Wang <[email protected]>
Cc: Yu Liao <[email protected]>
Cc: Phil Auld <[email protected]>
Cc: Paul Gortmaker<[email protected]>
Cc: Alex Belits <[email protected]>
Signed-off-by: Paul E. McKenney <[email protected]>
Reviewed-by: Nicolas Saenz Julienne <[email protected]>
Tested-by: Nicolas Saenz Julienne <[email protected]>

include/linux/rcupdate.h

@@ -112,6 +112,12 @@ 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);

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();
 		}
 		/*

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);
 }