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Date:   Wed, 12 Aug 2020 18:18:28 +1000
From:   Nicholas Piggin <npiggin@...il.com>
To:     peterz@...radead.org
Cc:     Alexey Kardashevskiy <aik@...abs.ru>, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>
Subject: Re: [PATCH 1/2] lockdep: improve current->(hard|soft)irqs_enabled
 synchronisation with actual irq state

Excerpts from peterz@...radead.org's message of August 7, 2020 9:11 pm:
> 
> What's wrong with something like this?
> 
> AFAICT there's no reason to actually try and add IRQ tracing here, it's
> just a hand full of instructions at the most.

Because we may want to use that in other places as well, so it would
be nice to have tracing.

Hmm... also, I thought NMI context was free to call local_irq_save/restore
anyway so the bug would still be there in those cases?

Thanks,
Nick

> 
> ---
> 
> diff --git a/arch/powerpc/include/asm/hw_irq.h b/arch/powerpc/include/asm/hw_irq.h
> index 3a0db7b0b46e..6be22c1838e2 100644
> --- a/arch/powerpc/include/asm/hw_irq.h
> +++ b/arch/powerpc/include/asm/hw_irq.h
> @@ -196,33 +196,6 @@ static inline bool arch_irqs_disabled(void)
>  		arch_local_irq_restore(flags);				\
>  	} while(0)
>  
> -#ifdef CONFIG_TRACE_IRQFLAGS
> -#define powerpc_local_irq_pmu_save(flags)			\
> -	 do {							\
> -		raw_local_irq_pmu_save(flags);			\
> -		trace_hardirqs_off();				\
> -	} while(0)
> -#define powerpc_local_irq_pmu_restore(flags)			\
> -	do {							\
> -		if (raw_irqs_disabled_flags(flags)) {		\
> -			raw_local_irq_pmu_restore(flags);	\
> -			trace_hardirqs_off();			\
> -		} else {					\
> -			trace_hardirqs_on();			\
> -			raw_local_irq_pmu_restore(flags);	\
> -		}						\
> -	} while(0)
> -#else
> -#define powerpc_local_irq_pmu_save(flags)			\
> -	do {							\
> -		raw_local_irq_pmu_save(flags);			\
> -	} while(0)
> -#define powerpc_local_irq_pmu_restore(flags)			\
> -	do {							\
> -		raw_local_irq_pmu_restore(flags);		\
> -	} while (0)
> -#endif  /* CONFIG_TRACE_IRQFLAGS */
> -
>  #endif /* CONFIG_PPC_BOOK3S */
>  
>  #ifdef CONFIG_PPC_BOOK3E
> diff --git a/arch/powerpc/include/asm/local.h b/arch/powerpc/include/asm/local.h
> index bc4bd19b7fc2..b357a35672b1 100644
> --- a/arch/powerpc/include/asm/local.h
> +++ b/arch/powerpc/include/asm/local.h
> @@ -32,9 +32,9 @@ static __inline__ void local_##op(long i, local_t *l)			\
>  {									\
>  	unsigned long flags;						\
>  									\
> -	powerpc_local_irq_pmu_save(flags);				\
> +	raw_powerpc_local_irq_pmu_save(flags);				\
>  	l->v c_op i;						\
> -	powerpc_local_irq_pmu_restore(flags);				\
> +	raw_powerpc_local_irq_pmu_restore(flags);				\
>  }
>  
>  #define LOCAL_OP_RETURN(op, c_op)					\
> @@ -43,9 +43,9 @@ static __inline__ long local_##op##_return(long a, local_t *l)		\
>  	long t;								\
>  	unsigned long flags;						\
>  									\
> -	powerpc_local_irq_pmu_save(flags);				\
> +	raw_powerpc_local_irq_pmu_save(flags);				\
>  	t = (l->v c_op a);						\
> -	powerpc_local_irq_pmu_restore(flags);				\
> +	raw_powerpc_local_irq_pmu_restore(flags);				\
>  									\
>  	return t;							\
>  }
> @@ -81,11 +81,11 @@ static __inline__ long local_cmpxchg(local_t *l, long o, long n)
>  	long t;
>  	unsigned long flags;
>  
> -	powerpc_local_irq_pmu_save(flags);
> +	raw_powerpc_local_irq_pmu_save(flags);
>  	t = l->v;
>  	if (t == o)
>  		l->v = n;
> -	powerpc_local_irq_pmu_restore(flags);
> +	raw_powerpc_local_irq_pmu_restore(flags);
>  
>  	return t;
>  }
> @@ -95,10 +95,10 @@ static __inline__ long local_xchg(local_t *l, long n)
>  	long t;
>  	unsigned long flags;
>  
> -	powerpc_local_irq_pmu_save(flags);
> +	raw_powerpc_local_irq_pmu_save(flags);
>  	t = l->v;
>  	l->v = n;
> -	powerpc_local_irq_pmu_restore(flags);
> +	raw_powerpc_local_irq_pmu_restore(flags);
>  
>  	return t;
>  }
> @@ -117,12 +117,12 @@ static __inline__ int local_add_unless(local_t *l, long a, long u)
>  	unsigned long flags;
>  	int ret = 0;
>  
> -	powerpc_local_irq_pmu_save(flags);
> +	raw_powerpc_local_irq_pmu_save(flags);
>  	if (l->v != u) {
>  		l->v += a;
>  		ret = 1;
>  	}
> -	powerpc_local_irq_pmu_restore(flags);
> +	raw_powerpc_local_irq_pmu_restore(flags);
>  
>  	return ret;
>  }
> 

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