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

walimis
2011-08-11T05:56:46Z

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.
>