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

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Date: Tue, 18 Jun 2024 12:02:34 +0200
From: Alexandre Ghiti <alex@...ti.fr>
To: Xu Lu <luxu.kernel@...edance.com>
Cc: Palmer Dabbelt <palmer@...belt.com>,
 Paul Walmsley <paul.walmsley@...ive.com>, aou@...s.berkeley.edu,
 linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [External] Re: [PATCH] riscv: Fix local irq restore when flags
 indicates irq disabled

On 18/06/2024 12:00, Xu Lu wrote:
> Hi Alex,
>
> I will send a new version later today.

Great, thanks, I'll make sure it lands in -fixes.

Sorry it did not get merged sooner.

Thanks,

Alex

>
> Thanks,
>
> Xu Lu
>
> On Tue, Jun 18, 2024 at 5:45 PM Alexandre Ghiti <alex@...ti.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@...edance.com> wrote:
>>>> On Wed, Aug 9, 2023 at 2:05 PM Palmer Dabbelt <palmer@...belt.com> wrote:
>>>>> On Tue, 25 Jul 2023 00:05:49 PDT (-0700), luxu.kernel@...edance.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@...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 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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