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

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Message-ID: <329b22c6-435c-424a-8211-b9a029b0897d@ghiti.fr>
Date: Tue, 18 Jun 2024 11:45:28 +0200
From: Alexandre Ghiti <alex@...ti.fr>
To: Xu Lu <luxu.kernel@...edance.com>, Palmer Dabbelt <palmer@...belt.com>
Cc: 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

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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> linux-riscv@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-riscv

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