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From:   "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
To:     Christophe Leroy <christophe.leroy@c-s.fr>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>
Cc:     linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v1 03/27] powerpc/mm: don't BUG() in slice_mask_for_size()
In-Reply-To: <f67363798e1ffb7603cd6619cb867563e4126d9a.1553076180.git.christophe.leroy@c-s.fr>
References: <cover.1553076180.git.christophe.leroy@c-s.fr> <f67363798e1ffb7603cd6619cb867563e4126d9a.1553076180.git.christophe.leroy@c-s.fr>
Date:   Thu, 11 Apr 2019 11:11:39 +0530
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Message-Id: <87lg0h3xpo.fsf@linux.ibm.com>
Sender: linux-kernel-owner@vger.kernel.org
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Christophe Leroy <christophe.leroy@c-s.fr> writes:

> When no mask is found for the page size, WARN() and return NULL
> instead of BUG()ing.
>
> Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
> ---
>  arch/powerpc/mm/slice.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/mm/slice.c b/arch/powerpc/mm/slice.c
> index aec91dbcdc0b..011d470ea340 100644
> --- a/arch/powerpc/mm/slice.c
> +++ b/arch/powerpc/mm/slice.c
> @@ -165,7 +165,8 @@ static struct slice_mask *slice_mask_for_size(struct mm_struct *mm, int psize)
>  	if (psize == MMU_PAGE_16G)
>  		return &mm->context.mask_16g;
>  #endif
> -	BUG();
> +	WARN_ON(true);
> +	return NULL;
>  }


Same here. There are not catching runtime errors. We should never find
that true. This is to catch mistakes during development changes. Switch
to VM_BUG_ON?


>  #elif defined(CONFIG_PPC_8xx)
>  static struct slice_mask *slice_mask_for_size(struct mm_struct *mm, int psize)
> @@ -178,7 +179,8 @@ static struct slice_mask *slice_mask_for_size(struct mm_struct *mm, int psize)
>  	if (psize == MMU_PAGE_8M)
>  		return &mm->context.mask_8m;
>  #endif
> -	BUG();
> +	WARN_ON(true);
> +	return NULL;
>  }
>  #else
>  #error "Must define the slice masks for page sizes supported by the platform"
> -- 
> 2.13.3