Subject: Re: [PATCH] powerpc: use local var instead of local_paca->irq_happened directly in __check_irq_replay

From: Wang Sheng-Hui <[email-masked]>
Date: Thu, 03 May 2012 13:51:20 +0800

On 2012年05月03日 12:22, Benjamin Herrenschmidt wrote:
> 
>> It should not as __check_irq_replay() should always be called
>> with interrupts hard disabled... Do you see any code path
>> where that is not the case ?
> 
> More specifically, your backtrace seems to indicate that
> __check_irq_repay() was called from arch_local_irq_restore() which
> should have done this before calling __check_irq_replay():
> 
> 	if (unlikely(irq_happened != PACA_IRQ_HARD_DIS))
> 		__hard_irq_disable();
> 
> Now, the only possibility that I can see for an interrupt to come in
> and trip the problem you observed would be if for some reason we
> had irq_happened set to PACA_IRQ_HARD_DIS while interrupts were
> not hard disabled.

I have a chance to notice that the value is 0x05, not just 0x01.
So I think this is not the case.

> 
> Can you try if removing the test (and thus unconditionally calling
> __hard_irq_disable()) fixes the problem for you ?
> 
> If that is the case, then we need to audit the code to figure out how we
> can end up with that bit in irq_happened set and interrupts hard
> enabled.
> 
> Something like may_hard_irq_enable() shouldn't cause it since it should
> only be called while hard disabled but adding a check in there might be
> worth it (something like WARN_ON(mfmsr() & MSR_EE)).
> 
> Cheers,
> Ben.
> 
>> Cheers,
>> Ben.
>>
>>> Signed-off-by: Wang Sheng-Hui <[email-masked]>
>>> ---
>>>  arch/powerpc/kernel/irq.c |   46 +++++++++++++++++++++++++++++---------------
>>>  1 files changed, 30 insertions(+), 16 deletions(-)
>>>
>>> diff --git a/arch/powerpc/kernel/irq.c b/arch/powerpc/kernel/irq.c
>>> index 5ec1b23..3d48b23 100644
>>> --- a/arch/powerpc/kernel/irq.c
>>> +++ b/arch/powerpc/kernel/irq.c
>>> @@ -137,15 +137,17 @@ static inline notrace int decrementer_check_overflow(void)
>>>   */
>>>  notrace unsigned int __check_irq_replay(void)
>>>  {
>>> +	unsigned int ret_val;
>>>  	/*
>>>  	 * We use local_paca rather than get_paca() to avoid all
>>>  	 * the debug_smp_processor_id() business in this low level
>>>  	 * function
>>>  	 */
>>> -	unsigned char happened = local_paca->irq_happened;
>>> +	unsigned char happened, irq_happened;
>>> +	happened = irq_happened = local_paca->irq_happened;
>>>  
>>>  	/* Clear bit 0 which we wouldn't clear otherwise */
>>> -	local_paca->irq_happened &= ~PACA_IRQ_HARD_DIS;
>>> +	irq_happened &= ~PACA_IRQ_HARD_DIS;
>>>  
>>>  	/*
>>>  	 * Force the delivery of pending soft-disabled interrupts on PS3.
>>> @@ -161,33 +163,45 @@ notrace unsigned int __check_irq_replay(void)
>>>  	 * decrementer itself rather than the paca irq_happened field
>>>  	 * in case we also had a rollover while hard disabled
>>>  	 */
>>> -	local_paca->irq_happened &= ~PACA_IRQ_DEC;
>>> -	if (decrementer_check_overflow())
>>> -		return 0x900;
>>> +	irq_happened &= ~PACA_IRQ_DEC;
>>> +	if (decrementer_check_overflow()) {
>>> +		ret_val = 0x900;
>>> +		goto replay;
>>> +	}
>>>  
>>>  	/* Finally check if an external interrupt happened */
>>> -	local_paca->irq_happened &= ~PACA_IRQ_EE;
>>> -	if (happened & PACA_IRQ_EE)
>>> -		return 0x500;
>>> +	irq_happened &= ~PACA_IRQ_EE;
>>> +	if (happened & PACA_IRQ_EE) {
>>> +		ret_val = 0x500;
>>> +		goto replay;
>>> +	}
>>>  
>>>  #ifdef CONFIG_PPC_BOOK3E
>>>  	/* Finally check if an EPR external interrupt happened
>>>  	 * this bit is typically set if we need to handle another
>>>  	 * "edge" interrupt from within the MPIC "EPR" handler
>>>  	 */
>>> -	local_paca->irq_happened &= ~PACA_IRQ_EE_EDGE;
>>> -	if (happened & PACA_IRQ_EE_EDGE)
>>> -		return 0x500;
>>> +	irq_happened &= ~PACA_IRQ_EE_EDGE;
>>> +	if (happened & PACA_IRQ_EE_EDGE) {
>>> +		ret_val = 0x500;
>>> +		goto replay;
>>> +	}
>>>  
>>> -	local_paca->irq_happened &= ~PACA_IRQ_DBELL;
>>> -	if (happened & PACA_IRQ_DBELL)
>>> -		return 0x280;
>>> +	irq_happened &= ~PACA_IRQ_DBELL;
>>> +	if (happened & PACA_IRQ_DBELL) {
>>> +		ret_val = 0x280;
>>> +		goto replay;
>>> +	}
>>>  #endif /* CONFIG_PPC_BOOK3E */
>>>  
>>>  	/* There should be nothing left ! */
>>> -	BUG_ON(local_paca->irq_happened != 0);
>>> +	BUG_ON(irq_happened != 0);
>>> +	ret_val = 0;
>>>  
>>> -	return 0;
>>> +replay:
>>> +	local_paca->irq_happened = irq_happened;
>>> +
>>> +	return ret_val;
>>>  }
>>>  
>>>  notrace void arch_local_irq_restore(unsigned long en)
>>
>>
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> 
>