[PATCH v8 5/8] entry: Add arch_irqentry_exit_need_resched() for arm64

[Jinjie Ruan]

Compared to the generic entry code, ARM64 does additional checks
when deciding to reschedule on return from interrupt. So introduce
arch_irqentry_exit_need_resched() in the need_resched()
condition of the generic raw_irqentry_exit_cond_resched(), with
a NOP default. This will allow ARM64 to implement the architecture
specific version for switching over to the generic entry code.

Suggested-by: Ada Couprie Diaz <ada.coupriediaz at arm.com>
Suggested-by: Mark Rutland <mark.rutland at arm.com>
Suggested-by: Kevin Brodsky <kevin.brodsky at arm.com>
Suggested-by: Thomas Gleixner <tglx at linutronix.de>
Signed-off-by: Jinjie Ruan <ruanjinjie at huawei.com>
---
 kernel/entry/common.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/kernel/entry/common.c b/kernel/entry/common.c
index 408d28b5179d..f62e1d1b2063 100644
--- a/kernel/entry/common.c
+++ b/kernel/entry/common.c
@@ -143,6 +143,20 @@ noinstr irqentry_state_t irqentry_enter(struct pt_regs *regs)
 	return ret;
 }
 
+/**
+ * arch_irqentry_exit_need_resched - Architecture specific need resched function
+ *
+ * Invoked from raw_irqentry_exit_cond_resched() to check if resched is needed.
+ * Defaults return true.
+ *
+ * The main purpose is to permit arch to avoid preemption of a task from an IRQ.
+ */
+static inline bool arch_irqentry_exit_need_resched(void);
+
+#ifndef arch_irqentry_exit_need_resched
+static inline bool arch_irqentry_exit_need_resched(void) { return true; }
+#endif
+
 void raw_irqentry_exit_cond_resched(void)
 {
 	if (!preempt_count()) {
@@ -150,7 +164,7 @@ void raw_irqentry_exit_cond_resched(void)
 		rcu_irq_exit_check_preempt();
 		if (IS_ENABLED(CONFIG_DEBUG_ENTRY))
 			WARN_ON_ONCE(!on_thread_stack());
-		if (need_resched())
+		if (need_resched() && arch_irqentry_exit_need_resched())
 			preempt_schedule_irq();
 	}
 }
-- 
2.34.1