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

From: Benjamin Herrenschmidt <[email-masked]>
Date: Thu, 03 May 2012 14:22:41 +1000

> 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.

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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