[External] Re: [PATCH] riscv: Fix local irq restore when flags indicates irq disabled

[Xu Lu]

Hi Alex,

I will send a new version later today.

Thanks,

Xu Lu

On Tue, Jun 18, 2024 at 5:45 PM Alexandre Ghiti <alex at ghiti.fr> wrote:
>
> Hi Xu Lu,
>
> On 24/08/2023 14:08, Xu Lu wrote:
> > On Wed, Aug 9, 2023 at 2:58 PM 旭路 <luxu.kernel at bytedance.com> wrote:
> >> On Wed, Aug 9, 2023 at 2:05 PM Palmer Dabbelt <palmer at dabbelt.com> wrote:
> >>> On Tue, 25 Jul 2023 00:05:49 PDT (-0700), luxu.kernel at 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 at 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 */
> > A gentle ping.
>
>
> This got lost but this is still correct and needed.
>
> Do you think you can respin a new version? Otherwise, I'll do it and
> keep you SoB.
>
> Thanks,
>
> Alex
>
>
> >
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