linux-kernel - Re: [PATCH] powerpc/mpic: Cleanup irq vector accounting

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Date:   Wed, 04 Jul 2018 23:27:15 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Bharat Bhushan <Bharat.Bhushan@....com>, benh@...nel.crashing.org,
        paulus@...ba.org, robh@...nel.org, geoff@...radead.org,
        tyreld@...ux.vnet.ibm.com, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org
Cc:     Bharat Bhushan <Bharat.Bhushan@....com>
Subject: Re: [PATCH] powerpc/mpic: Cleanup irq vector accounting

Bharat Bhushan <Bharat.Bhushan@....com> writes:

> Available vector space accounts ipis and timer interrupts
> while spurious vector was not accounted.

OK. What is the symptom of that? Nothing? Total system crash?

Looks like this can be tagged:

Fixes: 0a4081641d72 ("powerpc/mpic: FSL MPIC error interrupt support.")

Which added the code that uses "12".

> Also later
> mpic_setup_error_int() escape one more vector, seemingly it
> assumes one spurious vector.

Ah right, I get it now.

So there is no bug. It's just a disagreement about whether the "intvec"
argument to mpic_setup_error_int() indicates the first number that's
free to use or the last number that has been allocated.

Right?

cheers

> Signed-off-by: Bharat Bhushan <Bharat.Bhushan@....com>
> ---
>  arch/powerpc/sysdev/fsl_mpic_err.c | 2 +-
>  arch/powerpc/sysdev/mpic.c         | 6 +++---
>  2 files changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/arch/powerpc/sysdev/fsl_mpic_err.c b/arch/powerpc/sysdev/fsl_mpic_err.c
> index 488ec45..2a98837 100644
> --- a/arch/powerpc/sysdev/fsl_mpic_err.c
> +++ b/arch/powerpc/sysdev/fsl_mpic_err.c
> @@ -76,7 +76,7 @@ int mpic_setup_error_int(struct mpic *mpic, int intvec)
>  	mpic->flags |= MPIC_FSL_HAS_EIMR;
>  	/* allocate interrupt vectors for error interrupts */
>  	for (i = MPIC_MAX_ERR - 1; i >= 0; i--)
> -		mpic->err_int_vecs[i] = --intvec;
> +		mpic->err_int_vecs[i] = intvec--;
>  
>  	return 0;
>  }
> diff --git a/arch/powerpc/sysdev/mpic.c b/arch/powerpc/sysdev/mpic.c
> index 1d4e0ef6..e098d1e 100644
> --- a/arch/powerpc/sysdev/mpic.c
> +++ b/arch/powerpc/sysdev/mpic.c
> @@ -1380,12 +1380,12 @@ struct mpic * __init mpic_alloc(struct device_node *node,
>  		 * global vector number space, as in case of ipis
>  		 * and timer interrupts.
>  		 *
> -		 * Available vector space = intvec_top - 12, where 12
> +		 * Available vector space = intvec_top - 13, where 13
>  		 * is the number of vectors which have been consumed by
> -		 * ipis and timer interrupts.
> +		 * ipis, timer interrupts and spurious.
>  		 */
>  		if (fsl_version >= 0x401) {
> -			ret = mpic_setup_error_int(mpic, intvec_top - 12);
> +			ret = mpic_setup_error_int(mpic, intvec_top - 13);
>  			if (ret)
>  				return NULL;
>  		}
> -- 
> 1.9.3