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 <[email protected]>
---
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);
}
#endif /* _ASM_RISCV_IRQFLAGS_H */
--
2.39.2 (Apple Git-143)
On Tue, 25 Jul 2023 00:05:49 PDT (-0700), [email protected] 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 <[email protected]>
> ---
> 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 */
On Wed, Aug 9, 2023 at 2:05 PM Palmer Dabbelt <[email protected]> wrote:
>
> On Tue, 25 Jul 2023 00:05:49 PDT (-0700), [email protected] 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 <[email protected]>
> > ---
> > 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 */