linux-kernel - Re: [PATCH v13 5/5] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE

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Message-ID: <59832353.1020600@intel.com>
Date:   Thu, 03 Aug 2017 21:21:23 +0800
From:   Wei Wang <wei.w.wang@...el.com>
To:     Pankaj Gupta <pagupta@...hat.com>
CC:     linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, kvm@...r.kernel.org,
        linux-mm@...ck.org, mst@...hat.com, mhocko@...nel.org,
        mawilcox@...rosoft.com, akpm@...ux-foundation.org,
        virtio-dev@...ts.oasis-open.org, david@...hat.com,
        cornelia huck <cornelia.huck@...ibm.com>,
        mgorman@...hsingularity.net, aarcange@...hat.com,
        amit shah <amit.shah@...hat.com>, pbonzini@...hat.com,
        liliang opensource <liliang.opensource@...il.com>,
        yang zhang wz <yang.zhang.wz@...il.com>,
        quan xu <quan.xu@...yun.com>
Subject: Re: [PATCH v13 5/5] virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_VQ

On 08/03/2017 09:05 PM, Pankaj Gupta wrote:
>> On 08/03/2017 04:13 PM, Pankaj Gupta wrote:
>>>> +        /* Allocate space for find_vqs parameters */
>>>> +        vqs = kcalloc(nvqs, sizeof(*vqs), GFP_KERNEL);
>>>> +        if (!vqs)
>>>> +                goto err_vq;
>>>> +        callbacks = kmalloc_array(nvqs, sizeof(*callbacks), GFP_KERNEL);
>>>> +        if (!callbacks)
>>>> +                goto err_callback;
>>>> +        names = kmalloc_array(nvqs, sizeof(*names), GFP_KERNEL);
>>>                       
>>>          is size here (integer) intentional?
>>
>> Sorry, I didn't get it. Could you please elaborate more?
> This is okay
>
>>
>>>> +        if (!names)
>>>> +                goto err_names;
>>>> +
>>>> +        callbacks[0] = balloon_ack;
>>>> +        names[0] = "inflate";
>>>> +        callbacks[1] = balloon_ack;
>>>> +        names[1] = "deflate";
>>>> +
>>>> +        i = 2;
>>>> +        if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
>>>> +                callbacks[i] = stats_request;
>>> just thinking if memory for callbacks[3] & names[3] is allocated?
>>
>> Yes, the above kmalloc_array allocated them.
> I mean we have created callbacks array for two entries 0,1?
>
> callbacks = kmalloc_array(nvqs, sizeof(*callbacks), GFP_KERNEL);
>
> But we are trying to access location '2' which is third:
>
>           i = 2;
> +        if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ)) {
> +                callbacks[i] = stats_request;      <---- callbacks[2]
> +                names[i] = "stats";                <----- names[2]
> +                i++;
> +        }
>
> I am missing anything obvious here?


Yes.
if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_STATS_VQ) is true
nvqs will be 3, that is, callbacks[2] is allocated.

Best,
Wei