Re: [PATCH -next v7 5/7] arm64: entry: Refactor preempt_schedule_irq() check code

[Ada Couprie Diaz <ada.coupriediaz@xxxxxxx>]

On 29/07/2025 02:54, Jinjie Ruan wrote:

> ARM64 requires an additional check whether to reschedule on return
> from interrupt. So add arch_irqentry_exit_need_resched() as the default
> NOP implementation and hook it up into the need_resched() condition in
> raw_irqentry_exit_cond_resched(). This allows ARM64 to implement
> the architecture specific version for switching over to
> the generic entry code.
>
> To align the structure of the code with irqentry_exit_cond_resched()
> from the generic entry code, hoist the need_irq_preemption()
> and IS_ENABLED() check earlier. And different preemption check functions
> are defined based on whether dynamic preemption is enabled.
>
> Suggested-by: Mark Rutland <mark.rutland@xxxxxxx>
> Suggested-by: Kevin Brodsky <kevin.brodsky@xxxxxxx>
> Suggested-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Signed-off-by: Jinjie Ruan <ruanjinjie@xxxxxxxxxx>
> ---
Unrelated to the other thread : I noticed that compiling this patch
with `allnoconfig` would fail :
- `raw_irqentry_exit_cond_resched` has no previous prototype,
  as it is defined within `#ifdef CONFIG_PREEMPTION`
- `irqentry_exit_cond_resched()` is not declared, as it is also within
  `#ifdef CONFIG_PREEMPTION`

The patch below fixes the issue, but introduces merge conflicts in
patches 6 and 7, plus the `#ifdef` needs to be moved accordingly
in patch 6 and the empty "without preemption" `irq_exit_cond_resched()`
needs to be removed in patch 7.

I hope this can be useful,
Ada

---
diff --git a/arch/arm64/include/asm/preempt.h 
b/arch/arm64/include/asm/preempt.h
index 0f0ba250efe8..d9aba8b1e466 100644
--- a/arch/arm64/include/asm/preempt.h
+++ b/arch/arm64/include/asm/preempt.h
@@ -103,6 +103,8 @@ void dynamic_irqentry_exit_cond_resched(void);
 #define irqentry_exit_cond_resched() raw_irqentry_exit_cond_resched()

 #endif /* CONFIG_PREEMPT_DYNAMIC */
+#else /* CONFIG_PREEMPTION */
+#define irqentry_exit_cond_resched() {}
 #endif /* CONFIG_PREEMPTION */

 #endif /* __ASM_PREEMPT_H */
diff --git a/arch/arm64/kernel/entry-common.c 
b/arch/arm64/kernel/entry-common.c
index 4f92664fd46c..abd7a315145e 100644
--- a/arch/arm64/kernel/entry-common.c
+++ b/arch/arm64/kernel/entry-common.c
@@ -661,6 +661,7 @@ static __always_inline void __el1_pnmi(struct 
pt_regs *regs,
        arm64_exit_nmi(regs, state);
 }

+#ifdef CONFIG_PREEMPTION
 void raw_irqentry_exit_cond_resched(void)
 {
        if (!preempt_count()) {
@@ -668,6 +669,7 @@ void raw_irqentry_exit_cond_resched(void)
                        preempt_schedule_irq();
        }
 }
+#endif

 #ifdef CONFIG_PREEMPT_DYNAMIC
 DEFINE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched);