netdev - RE: [PATCH] virtio-net: fix the kzalloc/kfree mismatch problem

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Message-ID: <36e8999c9a5d443990384183265b25ee@huawei.com>
Date:   Tue, 25 May 2021 01:11:43 +0000
From:   "Guodeqing (A)" <geffrey.guo@...wei.com>
To:     Jason Wang <jasowang@...hat.com>,
        Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
CC:     "davem@...emloft.net" <davem@...emloft.net>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Max Gurtovoy <mgurtovoy@...dia.com>,
        "mst@...hat.com" <mst@...hat.com>
Subject: RE: [PATCH] virtio-net: fix the kzalloc/kfree mismatch problem



> -----Original Message-----
> From: Jason Wang [mailto:jasowang@...hat.com]
> Sent: Monday, May 24, 2021 10:37
> To: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>; Guodeqing (A)
> <geffrey.guo@...wei.com>
> Cc: davem@...emloft.net; kuba@...nel.org; virtualization@...ts.linux-
> foundation.org; netdev@...r.kernel.org; Max Gurtovoy
> <mgurtovoy@...dia.com>; mst@...hat.com
> Subject: Re: [PATCH] virtio-net: fix the kzalloc/kfree mismatch problem
> 
> 
> 在 2021/5/24 上午10:06, Xuan Zhuo 写道:
> > On Mon, 24 May 2021 01:48:53 +0000, Guodeqing (A)
> <geffrey.guo@...wei.com> wrote:
> >>
> >>> -----Original Message-----
> >>> From: Max Gurtovoy [mailto:mgurtovoy@...dia.com]
> >>> Sent: Sunday, May 23, 2021 15:25
> >>> To: Guodeqing (A) <geffrey.guo@...wei.com>; mst@...hat.com
> >>> Cc: jasowang@...hat.com; davem@...emloft.net; kuba@...nel.org;
> >>> virtualization@...ts.linux-foundation.org; netdev@...r.kernel.org
> >>> Subject: Re: [PATCH] virtio-net: fix the kzalloc/kfree mismatch problem
> >>>
> >>>
> >>> On 5/22/2021 11:02 AM, guodeqing wrote:
> >>>> If the virtio_net device does not suppurt the ctrl queue feature, the
> >>>> vi->ctrl was not allocated, so there is no need to free it.
> >>> you don't need this check.
> >>>
> >>> from kfree doc:
> >>>
> >>> "If @objp is NULL, no operation is performed."
> >>>
> >>> This is not a bug. I've set vi->ctrl to be NULL in case !vi->has_cvq.
> >>>
> >>>
> >>    yes,  this is not a bug, the patch is just a optimization, because the vi-
> >ctrl maybe
> >>    be freed which  was not allocated, this may give people a
> misunderstanding.
> >>    Thanks.
> >
> > I think it may be enough to add a comment, and the code does not need to
> be
> > modified.
> >
> > Thanks.
> 
> 
> Or even just leave the current code as is. A lot of kernel codes was
> wrote under the assumption that kfree() should deal with NULL.
> 
> Thanks
> 
> 

ok, I see. Is it necessary to set the vi->ctrl value to null,because the vi->ctrl value is set
to zero in the alloc_etherdev_mq function by kzalloc.

Thanks.
> >
> >>>> Here I adjust the initialization sequence and the check of vi->has_cvq
> >>>> to slove this problem.
> >>>>
> >>>> Fixes: 	122b84a1267a ("virtio-net: don't allocate control_buf if not
> >>> supported")
> >>>> Signed-off-by: guodeqing <geffrey.guo@...wei.com>
> >>>> ---
> >>>>    drivers/net/virtio_net.c | 20 ++++++++++----------
> >>>>    1 file changed, 10 insertions(+), 10 deletions(-)
> >>>>
> >>>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c index
> >>>> 9b6a4a875c55..894f894d3a29 100644
> >>>> --- a/drivers/net/virtio_net.c
> >>>> +++ b/drivers/net/virtio_net.c
> >>>> @@ -2691,7 +2691,8 @@ static void virtnet_free_queues(struct
> >>>> virtnet_info *vi)
> >>>>
> >>>>    	kfree(vi->rq);
> >>>>    	kfree(vi->sq);
> >>>> -	kfree(vi->ctrl);
> >>>> +	if (vi->has_cvq)
> >>>> +		kfree(vi->ctrl);
> >>>>    }
> >>>>
> >>>>    static void _free_receive_bufs(struct virtnet_info *vi) @@ -2870,13
> >>>> +2871,6 @@ static int virtnet_alloc_queues(struct virtnet_info *vi)
> >>>>    {
> >>>>    	int i;
> >>>>
> >>>> -	if (vi->has_cvq) {
> >>>> -		vi->ctrl = kzalloc(sizeof(*vi->ctrl), GFP_KERNEL);
> >>>> -		if (!vi->ctrl)
> >>>> -			goto err_ctrl;
> >>>> -	} else {
> >>>> -		vi->ctrl = NULL;
> >>>> -	}
> >>>>    	vi->sq = kcalloc(vi->max_queue_pairs, sizeof(*vi->sq), GFP_KERNEL);
> >>>>    	if (!vi->sq)
> >>>>    		goto err_sq;
> >>>> @@ -2884,6 +2878,12 @@ static int virtnet_alloc_queues(struct
> >>> virtnet_info *vi)
> >>>>    	if (!vi->rq)
> >>>>    		goto err_rq;
> >>>>
> >>>> +	if (vi->has_cvq) {
> >>>> +		vi->ctrl = kzalloc(sizeof(*vi->ctrl), GFP_KERNEL);
> >>>> +		if (!vi->ctrl)
> >>>> +			goto err_ctrl;
> >>>> +	}
> >>>> +
> >>>>    	INIT_DELAYED_WORK(&vi->refill, refill_work);
> >>>>    	for (i = 0; i < vi->max_queue_pairs; i++) {
> >>>>    		vi->rq[i].pages = NULL;
> >>>> @@ -2902,11 +2902,11 @@ static int virtnet_alloc_queues(struct
> >>>> virtnet_info *vi)
> >>>>
> >>>>    	return 0;
> >>>>
> >>>> +err_ctrl:
> >>>> +	kfree(vi->rq);
> >>>>    err_rq:
> >>>>    	kfree(vi->sq);
> >>>>    err_sq:
> >>>> -	kfree(vi->ctrl);
> >>>> -err_ctrl:
> >>>>    	return -ENOMEM;
> >>>>    }
> >>>>