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

[Xu Lu]

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.