linux-kernel - Re: [PATCH] riscv: Fix local irq restore when flags indicates irq disabled

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Date: Tue, 18 Jun 2024 13:06:39 +0100
From: Mark Rutland <mark.rutland@....com>
To: Xu Lu <luxu.kernel@...edance.com>
Cc: alex@...ti.fr, paul.walmsley@...ive.com, palmer@...belt.com,
	aou@...s.berkeley.edu, linux-riscv@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] riscv: Fix local irq restore when flags indicates irq
 disabled

On Tue, Jun 18, 2024 at 06:38:03PM +0800, Xu Lu wrote:
> When arch_local_irq_restore() is called with flags indicating irqs
> disabled, we need to clear SR_IE bit in CSR_STATUS, whereas current
> implementation based on csr_set() function only sets SR_IE bit of
> CSR_STATUS when SR_IE bit of flags is high and does nothing when
> SR_IE bit of flags is low.

That shouldn't matter; arch_local_irq_restore() should *never* be called
from a context with IRQs enabled, and so arch_local_irq_restore() never
needs to disable IRQs. Either it enables IRQs or it leaves IRQs
disabled, but it never needs to explicitly disable IRQs.

See CONFIG_DEBUG_IRQFLAGS and the commit that introduced it:

  997acaf6b4b59c6a ("lockdep: report broken irq restoration")

I don't believe this patch is necessary.

Mark.

> 
> This commit supplies csr clear operation when calling irq restore
> function with flags indicating irq disabled.
> 
> Fixes: 6d60b6ee0c97 ("RISC-V: Device, timer, IRQs, and the SBI")
> Signed-off-by: Xu Lu <luxu.kernel@...edance.com>
> ---
>  arch/riscv/include/asm/irqflags.h | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/riscv/include/asm/irqflags.h b/arch/riscv/include/asm/irqflags.h
> index 6fd8cbfcfcc7..f3aad7bfadb7 100644
> --- a/arch/riscv/include/asm/irqflags.h
> +++ b/arch/riscv/include/asm/irqflags.h
> @@ -48,7 +48,10 @@ static inline int arch_irqs_disabled(void)
>  /* set interrupt enabled status */
>  static inline void arch_local_irq_restore(unsigned long flags)
>  {
> -	csr_set(CSR_STATUS, flags & SR_IE);
> +	if (flags & SR_IE)
> +		csr_set(CSR_STATUS, SR_IE);
> +	else
> +		csr_clear(CSR_STATUS, SR_IE);
>  }
>  
>  #endif /* _ASM_RISCV_IRQFLAGS_H */
> -- 
> 2.20.1
> 
>