linux-kernel - Re: [PATCH v1 01/27] powerpc/mm: Don't BUG() in hugepd

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Date:   Thu, 11 Apr 2019 11:09:15 +0530
From:   "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
To:     Christophe Leroy <christophe.leroy@....fr>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v1 01/27] powerpc/mm: Don't BUG() in hugepd_page()

Christophe Leroy <christophe.leroy@....fr> writes:

> Don't BUG(), just warn and return NULL.
> If the NULL value is not handled, it will get catched anyway.
>
> Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
> ---
>  arch/powerpc/include/asm/hugetlb.h | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/hugetlb.h b/arch/powerpc/include/asm/hugetlb.h
> index 8d40565ad0c3..48c29686c78e 100644
> --- a/arch/powerpc/include/asm/hugetlb.h
> +++ b/arch/powerpc/include/asm/hugetlb.h
> @@ -14,7 +14,8 @@
>   */
>  static inline pte_t *hugepd_page(hugepd_t hpd)
>  {
> -	BUG_ON(!hugepd_ok(hpd));
> +	if (WARN_ON(!hugepd_ok(hpd)))
> +		return NULL;

We should not find that true. That BUG_ON was there to catch errors
when changing pte formats. May be switch that VM_BUG_ON()? 

>  	/*
>  	 * We have only four bits to encode, MMU page size
>  	 */
> @@ -42,7 +43,8 @@ static inline void flush_hugetlb_page(struct vm_area_struct *vma,
>  
>  static inline pte_t *hugepd_page(hugepd_t hpd)
>  {
> -	BUG_ON(!hugepd_ok(hpd));
> +	if (WARN_ON(!hugepd_ok(hpd)))
> +		return NULL;
>  #ifdef CONFIG_PPC_8xx
>  	return (pte_t *)__va(hpd_val(hpd) & ~HUGEPD_SHIFT_MASK);
>  #else
> -- 
> 2.13.3