linux-kernel - Re: [PATCH] s390/hypfs: Use kmalloc_array() in diag0c

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Date:   Thu, 1 Sep 2016 17:39:02 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Heiko Carstens <heiko.carstens@...ibm.com>,
        SF Markus Elfring <elfring@...rs.sourceforge.net>
Cc:     linux-s390@...r.kernel.org,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Michael Holzheu <holzheu@...ux.vnet.ibm.com>,
        LKML <linux-kernel@...r.kernel.org>,
        kernel-janitors@...r.kernel.org,
        Julia Lawall <julia.lawall@...6.fr>
Subject: Re: [PATCH] s390/hypfs: Use kmalloc_array() in diag0c_store()



On 01/09/2016 12:32, Heiko Carstens wrote:
> On Thu, Sep 01, 2016 at 11:38:15AM +0200, SF Markus Elfring wrote:
>> From: Markus Elfring <elfring@...rs.sourceforge.net>
>> Date: Thu, 1 Sep 2016 11:30:58 +0200
>>
>> A multiplication for the size determination of a memory allocation
>> indicated that an array data structure should be processed.
>> Thus use the corresponding function "kmalloc_array".
>>
>> This issue was detected by using the Coccinelle software.
>>
>> Signed-off-by: Markus Elfring <elfring@...rs.sourceforge.net>
>> ---
>>  arch/s390/hypfs/hypfs_diag0c.c | 4 +++-
>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/s390/hypfs/hypfs_diag0c.c b/arch/s390/hypfs/hypfs_diag0c.c
>> index 0f1927c..61418a8 100644
>> --- a/arch/s390/hypfs/hypfs_diag0c.c
>> +++ b/arch/s390/hypfs/hypfs_diag0c.c
>> @@ -48,7 +48,9 @@ static void *diag0c_store(unsigned int *count)
>>  
>>  	get_online_cpus();
>>  	cpu_count = num_online_cpus();
>> -	cpu_vec = kmalloc(sizeof(*cpu_vec) * num_possible_cpus(), GFP_KERNEL);
>> +	cpu_vec = kmalloc_array(num_possible_cpus(),
>> +				sizeof(*cpu_vec),
>> +				GFP_KERNEL);
> 
> How does this improve the situation? For any real life scenario this can't
> overflow, but it does add an extra (pointless) runtime check, since
> num_possible_cpus() is not a compile time constant.
> 
> So, why is this an "issue"?

It's not an issue but I for one still prefer consistent use of
kmalloc_array and kcalloc.

Paolo