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

[Mark Rutland <mark.rutland@xxxxxxx>]

On Tue, Jul 29, 2025 at 09:54:54AM +0800, 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>
> ---
>  arch/arm64/include/asm/preempt.h |  4 ++++
>  arch/arm64/kernel/entry-common.c | 35 ++++++++++++++++++--------------
>  kernel/entry/common.c            | 16 ++++++++++++++-
>  3 files changed, 39 insertions(+), 16 deletions(-)

Can you please split the change to kernel/entry/common.c into a separate
patch? That doesn't depend on the arm64-specific changes, and it'll make
it easier to handle any conflcits when merging this.

Mark.

> 
> diff --git a/arch/arm64/include/asm/preempt.h 
> b/arch/arm64/include/asm/preempt.h
> index 0159b625cc7f..0f0ba250efe8 100644
> --- a/arch/arm64/include/asm/preempt.h
> +++ b/arch/arm64/include/asm/preempt.h
> @@ -85,6 +85,7 @@ static inline bool should_resched(int preempt_offset)
>  void preempt_schedule(void);
>  void preempt_schedule_notrace(void);
>  
> +void raw_irqentry_exit_cond_resched(void);
>  #ifdef CONFIG_PREEMPT_DYNAMIC
>  
>  DECLARE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched);
> @@ -92,11 +93,14 @@ void dynamic_preempt_schedule(void);
>  #define __preempt_schedule()         dynamic_preempt_schedule()
>  void dynamic_preempt_schedule_notrace(void);
>  #define __preempt_schedule_notrace() dynamic_preempt_schedule_notrace()
> +void dynamic_irqentry_exit_cond_resched(void);
> +#define irqentry_exit_cond_resched() dynamic_irqentry_exit_cond_resched()
>  
>  #else /* CONFIG_PREEMPT_DYNAMIC */
>  
>  #define __preempt_schedule()         preempt_schedule()
>  #define __preempt_schedule_notrace() preempt_schedule_notrace()
> +#define irqentry_exit_cond_resched() raw_irqentry_exit_cond_resched()
>  
>  #endif /* CONFIG_PREEMPT_DYNAMIC */
>  #endif /* CONFIG_PREEMPTION */
> diff --git a/arch/arm64/kernel/entry-common.c 
> b/arch/arm64/kernel/entry-common.c
> index 7c2299c1ba79..4f92664fd46c 100644
> --- a/arch/arm64/kernel/entry-common.c
> +++ b/arch/arm64/kernel/entry-common.c
> @@ -285,19 +285,8 @@ static void noinstr arm64_exit_el1_dbg(struct pt_regs 
> *regs,
>               lockdep_hardirqs_on(CALLER_ADDR0);
>  }
>  
> -#ifdef CONFIG_PREEMPT_DYNAMIC
> -DEFINE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched);
> -#define need_irq_preemption() \
> -     (static_branch_unlikely(&sk_dynamic_irqentry_exit_cond_resched))
> -#else
> -#define need_irq_preemption()        (IS_ENABLED(CONFIG_PREEMPTION))
> -#endif
> -
>  static inline bool arm64_preempt_schedule_irq(void)
>  {
> -     if (!need_irq_preemption())
> -             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
> @@ -672,6 +661,24 @@ static __always_inline void __el1_pnmi(struct pt_regs 
> *regs,
>       arm64_exit_nmi(regs, state);
>  }
>  
> +void raw_irqentry_exit_cond_resched(void)
> +{
> +     if (!preempt_count()) {
> +             if (need_resched() && arm64_preempt_schedule_irq())
> +                     preempt_schedule_irq();
> +     }
> +}
> +
> +#ifdef CONFIG_PREEMPT_DYNAMIC
> +DEFINE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched);
> +void dynamic_irqentry_exit_cond_resched(void)
> +{
> +     if (!static_branch_unlikely(&sk_dynamic_irqentry_exit_cond_resched))
> +             return;
> +     raw_irqentry_exit_cond_resched();
> +}
> +#endif
> +
>  static __always_inline void __el1_irq(struct pt_regs *regs,
>                                     void (*handler)(struct pt_regs *))
>  {
> @@ -681,10 +688,8 @@ static __always_inline void __el1_irq(struct pt_regs 
> *regs,
>       do_interrupt_handler(regs, handler);
>       irq_exit_rcu();
>  
> -     if (!preempt_count() && need_resched()) {
> -             if (arm64_preempt_schedule_irq())
> -                     preempt_schedule_irq();
> -     }
> +     if (IS_ENABLED(CONFIG_PREEMPTION))
> +             irqentry_exit_cond_resched();
>  
>       exit_to_kernel_mode(regs, state);
>  }
> diff --git a/kernel/entry/common.c b/kernel/entry/common.c
> index b82032777310..4aa9656fa1b4 100644
> --- a/kernel/entry/common.c
> +++ b/kernel/entry/common.c
> @@ -142,6 +142,20 @@ 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 need resched.
> + * Defaults return true.
> + *
> + * The main purpose is to permit arch to skip preempt 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()) {
> @@ -149,7 +163,7 @@ 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
>