diff mbox series

riscv: Fix local irq restore when flags indicates irq disabled

Message ID 20230725070549.89810-1-luxu.kernel@bytedance.com
State New
Headers
Series riscv: Fix local irq restore when flags indicates irq disabled |

Commit Message

Xu Lu July 25, 2023, 7:05 a.m. UTC 
  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.

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@bytedance.com>
---
 arch/riscv/include/asm/irqflags.h | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

Comments

Palmer Dabbelt Aug. 9, 2023, 6:05 a.m. UTC | #1 
On Tue, 25 Jul 2023 00:05:49 PDT (-0700), luxu.kernel@bytedance.com 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.
>
> 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@bytedance.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 08d4d6a5b7e9..7c31fc3c3559 100644
> --- a/arch/riscv/include/asm/irqflags.h
> +++ b/arch/riscv/include/asm/irqflags.h
> @@ -49,7 +49,10 @@ 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);

Unless I'm missing something, the original version is correct: 
local_irq_restore() must be paired with a local_irq_save(), so we can 
only get here with interrupts disabled.

>  }
>
>  #endif /* _ASM_RISCV_IRQFLAGS_H */
Xu Lu Aug. 9, 2023, 6:58 a.m. UTC | #2 
On Wed, Aug 9, 2023 at 2:05 PM Palmer Dabbelt <palmer@dabbelt.com> wrote:
>
> On Tue, 25 Jul 2023 00:05:49 PDT (-0700), luxu.kernel@bytedance.com 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.
> >
> > 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@bytedance.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 08d4d6a5b7e9..7c31fc3c3559 100644
> > --- a/arch/riscv/include/asm/irqflags.h
> > +++ b/arch/riscv/include/asm/irqflags.h
> > @@ -49,7 +49,10 @@ 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);
>
> Unless I'm missing something, the original version is correct:
> local_irq_restore() must be paired with a local_irq_save(), so we can
> only get here with interrupts disabled.

Yes, it is correct if local_irq_save() is called when irq is enabled before.
The flags returned will be SR_IE. And it is safe to call local_irq_restore()
with flag SR_IE in any case.

However, if local_irq_save() is called when irq is disabled. The SR_IE bit of
flag returned is clear. If some code between local_irq_save() and
local_irq_restore() reenables irq, causing the SR_IE bit of CSR_STATUS
back to 1, then local_irq_restore() can not restore irq status back to disabled.

Here is an example in existing driver (may not belong to riscv arch) in
drivers/net/wireless/realtek/rtlwifi/rtl8723ae/hw.c. The pseudo code
behaves like:

int rtl8723e_hw_init(struct ieee80211_hw *hw)
{
     int err;
     unsigned long flags;
     ...
     local_irq_save_flags(flags);
     local_irq_enable();
     ...
     local_irq_restore(flags);
     ...
     return err;
}


>
> >  }
> >
> >  #endif /* _ASM_RISCV_IRQFLAGS_H */
diff mbox series

Patch

diff --git a/arch/riscv/include/asm/irqflags.h b/arch/riscv/include/asm/irqflags.h
index 08d4d6a5b7e9..7c31fc3c3559 100644
--- a/arch/riscv/include/asm/irqflags.h
+++ b/arch/riscv/include/asm/irqflags.h
@@ -49,7 +49,10 @@  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 */