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Subject: Re: [PATCH v1 01/27] powerpc/mm: Don't BUG() in hugepd_page()
To:     "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Michael Ellerman <mpe@ellerman.id.au>
Cc:     linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org
References: <cover.1553076180.git.christophe.leroy@c-s.fr>
 <9d6b0fe78346ff8e81a969a75a616bab59bc5cf5.1553076180.git.christophe.leroy@c-s.fr>
 <87r2a93xto.fsf@linux.ibm.com>
From:   Christophe Leroy <christophe.leroy@c-s.fr>
Message-ID: <bdeba4a0-451e-ab57-d844-197d7c8ae761@c-s.fr>
Date:   Wed, 24 Apr 2019 16:09:33 +0200
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Le 11/04/2019 à 07:39, Aneesh Kumar K.V a écrit :
> Christophe Leroy <christophe.leroy@c-s.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@c-s.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()?

Ok, I'll switch to VM_BUG_ON()

Christophe

> 
>>   	/*
>>   	 * 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