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Message-ID: <aJsh5oM3CoUELkvY@J2N7QTR9R3>
Date: Tue, 12 Aug 2025 12:13:42 +0100
From: Mark Rutland <mark.rutland@....com>
To: Jinjie Ruan <ruanjinjie@...wei.com>
Cc: catalin.marinas@....com, will@...nel.org, oleg@...hat.com,
sstabellini@...nel.org, puranjay@...nel.org, broonie@...nel.org,
mbenes@...e.cz, ryan.roberts@....com, akpm@...ux-foundation.org,
chenl311@...natelecom.cn, ada.coupriediaz@....com,
anshuman.khandual@....com, kristina.martsenko@....com,
liaochang1@...wei.com, ardb@...nel.org, leitao@...ian.org,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
xen-devel@...ts.xenproject.org
Subject: Re: [PATCH -next v7 5/7] arm64: entry: Refactor
preempt_schedule_irq() check code
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@....com>
> Suggested-by: Kevin Brodsky <kevin.brodsky@....com>
> Suggested-by: Thomas Gleixner <tglx@...utronix.de>
> Signed-off-by: Jinjie Ruan <ruanjinjie@...wei.com>
> ---
> 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
>
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