linux-kernel - Re: [PATCH] powerpc/highmem: change BUG_ON() to WARN

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Date:   Thu, 21 Mar 2019 07:00:04 +0100
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH] powerpc/highmem: change BUG_ON() to WARN_ON()



Le 21/03/2019 à 06:29, Michael Ellerman a écrit :
> Christophe Leroy <christophe.leroy@....fr> writes:
>> In arch/powerpc/mm/highmem.c, BUG_ON() is called only when
>> CONFIG_DEBUG_HIGHMEM is selected, this means the BUG_ON() is
>> not vital and can be replaced by a a WARN_ON
>>
>> At the sametime, use IS_ENABLED() instead of #ifdef to clean a bit.
>>
>> Signed-off-by: Christophe Leroy <christophe.leroy@....fr>
>> ---
>>   arch/powerpc/mm/highmem.c | 12 ++++--------
>>   1 file changed, 4 insertions(+), 8 deletions(-)
>>
>> diff --git a/arch/powerpc/mm/highmem.c b/arch/powerpc/mm/highmem.c
>> index 82a0e37557a5..b68c9f20fbdf 100644
>> --- a/arch/powerpc/mm/highmem.c
>> +++ b/arch/powerpc/mm/highmem.c
>> @@ -56,7 +54,7 @@ EXPORT_SYMBOL(kmap_atomic_prot);
>>   void __kunmap_atomic(void *kvaddr)
>>   {
>>   	unsigned long vaddr = (unsigned long) kvaddr & PAGE_MASK;
>> -	int type __maybe_unused;
>> +	int type;
> 
> Why don't we move type into the block below.

Yes you're right, when Mathieu introduced the __maybe_unused, I was 
wrongly thinging that kmap_atomic_idx() was doing something important 
that had to be done also when DEBUG was not selected, but indeed it does 
nothing else than returning the type.

I'll send a new patch.

Christophe

> 
> eg:
> 
>> @@ -66,12 +64,11 @@ void __kunmap_atomic(void *kvaddr)
>>   
> -  	type = kmap_atomic_idx();
>>   
>> -#ifdef CONFIG_DEBUG_HIGHMEM
>> -	{
>> +	if (IS_ENABLED(CONFIG_DEBUG_HIGHMEM)) {
>    		int type = kmap_atomic_idx();
>>   		unsigned int idx;
>>   
>>   		idx = type + KM_TYPE_NR * smp_processor_id();
>> -		BUG_ON(vaddr != __fix_to_virt(FIX_KMAP_BEGIN + idx));
>> +		WARN_ON(vaddr != __fix_to_virt(FIX_KMAP_BEGIN + idx));
> 
> 
> cheers
>