[PATCH -next v6 5/8] arm64: entry: Use preempt_count() and need_resched() helper

[Jinjie Ruan]

The generic entry code uses preempt_count() and need_resched() helpers to
check if it should do preempt_schedule_irq(). Currently, arm64 use its own
check logic, that is "READ_ONCE(current_thread_info()->preempt_count == 0",
which is equivalent to "preempt_count() == 0 && need_resched()".

In preparation for moving arm64 over to the generic entry code, use
these helpers to replace arm64's own code and move it ahead.

No functional changes.

Signed-off-by: Jinjie Ruan <ruanjinjie at huawei.com>
---
v6:
- Update the commit message.
- Move this ahead before we change the preemption logic to
  preempt non-IRQ exceptions.
---
 arch/arm64/kernel/entry-common.c | 14 ++++----------
 1 file changed, 4 insertions(+), 10 deletions(-)

diff --git a/arch/arm64/kernel/entry-common.c b/arch/arm64/kernel/entry-common.c
index 94e4132213ce..dceef4cb140b 100644
--- a/arch/arm64/kernel/entry-common.c
+++ b/arch/arm64/kernel/entry-common.c
@@ -294,14 +294,6 @@ static inline bool arm64_preempt_schedule_irq(void)
 	if (!need_irq_preemption())
 		return false;
 
-	/*
-	 * Note: thread_info::preempt_count includes both thread_info::count
-	 * and thread_info::need_resched, and is not equivalent to
-	 * preempt_count().
-	 */
-	if (READ_ONCE(current_thread_info()->preempt_count) != 0)
-		return false;
-
 	/*
 	 * DAIF.DA are cleared at the start of IRQ/FIQ handling, and when GIC
 	 * priority masking is used the GIC irqchip driver will clear DAIF.IF
@@ -593,8 +585,10 @@ static __always_inline void __el1_irq(struct pt_regs *regs,
 	do_interrupt_handler(regs, handler);
 	irq_exit_rcu();
 
-	if (arm64_preempt_schedule_irq())
-		preempt_schedule_irq();
+	if (!preempt_count() && need_resched()) {
+		if (arm64_preempt_schedule_irq())
+			preempt_schedule_irq();
+	}
 
 	exit_to_kernel_mode(regs, state);
 }
-- 
2.34.1