Re: [PATCH 1/4] KVM-S390: Improve determination of sizes in kvm_s390_import_bp_data()

Paolo Bonzini
2016-08-18T09:48:17Z

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@users.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@users.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
>>
>