Re: [PATCH 2/3] kvm tools: check negative value of num_pages

[walimis <walimisdev@gmail.com>]

On Thu, Aug 11, 2011 at 08:37:01AM +0300, Sasha Levin wrote:
>On Thu, 2011-08-11 at 13:07 +0800, Liming Wang wrote:
>> If num_pages is negative, balloon will make kernel crash with
>> "out of memory". So we check this value to avoid it to be negative.
>> 
>> Signed-off-by: Liming Wang <walimisdev@gmail.com>
>> ---
>>  tools/kvm/virtio/balloon.c |    7 ++++++-
>>  1 files changed, 6 insertions(+), 1 deletions(-)
>> 
>> diff --git a/tools/kvm/virtio/balloon.c b/tools/kvm/virtio/balloon.c
>> index 854d04b..0223ee4 100644
>> --- a/tools/kvm/virtio/balloon.c
>> +++ b/tools/kvm/virtio/balloon.c
>> @@ -222,8 +222,13 @@ static void handle_sigmem(int sig)
>>  {
>>  	if (sig == SIGKVMADDMEM)
>>  		bdev.config.num_pages += 256;
>> -	else
>> +	else {
>>  		bdev.config.num_pages -= 256;
>> +		if ((s32)bdev.config.num_pages < 0){
>
>imo it's worth doing this check before the decrement instead of casting
>to signed here.
You mean that check whether num_pages less than 256 or equal to 0?

>
>you also need to wrap the 'if ()' with parenthesis if you add them to
>the 'else' case.
Sorry, I'm not clear what that does mean?

walimis
>
>> +			bdev.config.num_pages = 0;
>> +			return;
>> +		}
>> +	}
>>  
>>  	/* Notify that the configuration space has changed */
>>  	bdev.isr = VIRTIO_PCI_ISR_CONFIG;
>
>-- 
>
>Sasha.
>