linux-kernel - Re: [PATCH] powerpc: Move a dereference below a NULL test

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Date:   Wed, 26 Sep 2018 22:42:23 +0800
From:   zhong jiang <zhongjiang@...wei.com>
To:     Michal Suchánek <msuchanek@...e.de>
CC:     <paulus@...ba.org>, <benh@...nel.crashing.org>,
        <mpe@...erman.id.au>, <linuxppc-dev@...ts.ozlabs.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] powerpc: Move a dereference below a NULL test

On 2018/9/26 22:22, Michal Suchánek wrote:
> On Wed, 26 Sep 2018 19:46:08 +0800
> zhong jiang <zhongjiang@...wei.com> wrote:
>
>> It is safe to move dereference below a NULL test.
>>
>> Signed-off-by: zhong jiang <zhongjiang@...wei.com>
>> ---
>>  arch/powerpc/kernel/cacheinfo.c | 5 ++---
>>  1 file changed, 2 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/powerpc/kernel/cacheinfo.c
>> b/arch/powerpc/kernel/cacheinfo.c index a8f20e5..7f19714 100644
>> --- a/arch/powerpc/kernel/cacheinfo.c
>> +++ b/arch/powerpc/kernel/cacheinfo.c
>> @@ -401,14 +401,13 @@ static struct cache
>> *cache_lookup_or_instantiate(struct device_node *node, struct cache
>> *cache; 
>>  	cache = cache_lookup_by_node(node);
>> +	if (!cache)
>> +		cache = cache_do_one_devnode(node, level);
>>  
>>  	WARN_ONCE(cache && cache->level != level,
> This has also null test so cache should be dereferenced only when
> non-null here.
:-[ ,  you're right.  I forget WARN_ONCE.  please ignore the patch.

Sincerely,
zhong jiang
> Thanks
>
> Michal
>
> .
>