linux-kernel - Re: [PATCH 1/4] KVM-S390: Improve determination of sizes in kvm_s390_import_bp

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Date:	Thu, 18 Aug 2016 11:48:17 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Julia Lawall <julia.lawall@...6.fr>, walter harms <wharms@....de>
Cc:	SF Markus Elfring <elfring@...rs.sourceforge.net>,
	kvm@...r.kernel.org, linux-s390@...r.kernel.org,
	Christian Bornträger <borntraeger@...ibm.com>,
	Cornelia Huck <cornelia.huck@...ibm.com>,
	David Hildenbrand <dahi@...ux.vnet.ibm.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Radim Krčmář <rkrcmar@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	kernel-janitors@...r.kernel.org
Subject: Re: [PATCH 1/4] KVM-S390: Improve determination of sizes in
 kvm_s390_import_bp_data()



On 18/08/2016 11:02, Julia Lawall wrote:
> 
> 
> On Thu, 18 Aug 2016, walter harms wrote:
> 
>>
>>
>> Am 17.08.2016 20:06, schrieb SF Markus Elfring:
>>> From: Markus Elfring <elfring@...rs.sourceforge.net>
>>> Date: Wed, 17 Aug 2016 18:29:04 +0200
>>>
>>> Replace the specification of data structures by pointer dereferences
>>> to make the corresponding size determination a bit safer according to
>>> the Linux coding style convention.
>>>
>>> Signed-off-by: Markus Elfring <elfring@...rs.sourceforge.net>
>>> ---
>>>  arch/s390/kvm/guestdbg.c | 6 +++---
>>>  1 file changed, 3 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/arch/s390/kvm/guestdbg.c b/arch/s390/kvm/guestdbg.c
>>> index d1f8241..b68db4b 100644
>>> --- a/arch/s390/kvm/guestdbg.c
>>> +++ b/arch/s390/kvm/guestdbg.c
>>> @@ -216,7 +216,7 @@ int kvm_s390_import_bp_data(struct kvm_vcpu *vcpu,
>>>  	else if (dbg->arch.nr_hw_bp > MAX_BP_COUNT)
>>>  		return -EINVAL;
>>>
>>> -	size = dbg->arch.nr_hw_bp * sizeof(struct kvm_hw_breakpoint);
>>> +	size = dbg->arch.nr_hw_bp * sizeof(*bp_data);
>>>  	bp_data = kmalloc(size, GFP_KERNEL);
>>>  	if (!bp_data) {
>>>  		ret = -ENOMEM;
>>> @@ -241,7 +241,7 @@ int kvm_s390_import_bp_data(struct kvm_vcpu *vcpu,
>>>  		}
>>>  	}
>>>
>>> -	size = nr_wp * sizeof(struct kvm_hw_wp_info_arch);
>>> +	size = nr_wp * sizeof(*wp_info);
>>>  	if (size > 0) {
>>>  		wp_info = kmalloc(size, GFP_KERNEL);
>>>  		if (!wp_info) {
>>> @@ -249,7 +249,7 @@ int kvm_s390_import_bp_data(struct kvm_vcpu *vcpu,
>>>  			goto error;
>>>  		}
>>>  	}
>>> -	size = nr_bp * sizeof(struct kvm_hw_bp_info_arch);
>>> +	size = nr_bp * sizeof(*bp_info);
>>>  	if (size > 0) {
>>>  		bp_info = kmalloc(size, GFP_KERNEL);
>>>  		if (!bp_info) {
>>
>>
>> IMHO the common pattern for kmalloc is
>>   bp_info = kmalloc( nr_bp * sizeof(*bp_info), GFP_KERNEL);
>>
>> i can not remember code with a check for size < 0, i guess it is here
>> to avoid an overflow ? since kmalloc takes a size_t argument this would cause
>> a malloc failure an can be ignored.
> 
> Shoudn't it be kcalloc?

Or kmalloc_array, since zeroing is not necessary.  Might be an idea for
a new Coccinelle script, like

- kmalloc (N * sizeof T, GFP)
+ kmalloc_array(N, sizeof T, GFP)

Thanks,

Paolo

> 
> julia
> 
>>
>>
>> just my 2 cents.
>> re,
>>  wh
>>
>