Subject: Re: [PATCH 1/2] arm64/entry: Fix involuntary preemption exception masking

From: Thomas Gleixner <[email-masked]>
Date: Tue, 24 Mar 2026 13:19:42 +0100

On Sun, Mar 22 2026 at 00:25, Thomas Gleixner wrote:
> On Fri, Mar 20 2026 at 17:31, Mark Rutland wrote:
> Looking at those details made me also look at this magic
> arch_irqentry_exit_need_resched() inline function. 
>
> 	/*
> 	 * 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
> 	 * using gic_arch_enable_irqs() for normal IRQs. If anything is set in
> 	 * DAIF we must have handled an NMI, so skip preemption.
> 	 */
> 	if (system_uses_irq_prio_masking() && read_sysreg(daif))
> 		return false;
>
> Why is this using irqentry_enter/exit() in the first place? 

Ah. The entry point does

          if (regs_irqs_disabled(regs))
          	do_nmi();
          else
                do_irq();

So you end up in do_irq() and eventually in the preemption path and need
that check to prevent scheduling. So that should be fine and obviously
won't hit the code path I outlined.

Thanks,

        tglx