netdev - Re: [PATCH net-next 4/6] vhost/net: remove vhost_net_page_frag

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Date: Mon, 8 Jan 2024 17:06:17 +0800
From: Yunsheng Lin <linyunsheng@...wei.com>
To: Alexander H Duyck <alexander.duyck@...il.com>, <davem@...emloft.net>,
	<kuba@...nel.org>, <pabeni@...hat.com>
CC: <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>, Jason Wang
	<jasowang@...hat.com>, "Michael S. Tsirkin" <mst@...hat.com>, Alexei
 Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, Jesper
 Dangaard Brouer <hawk@...nel.org>, John Fastabend <john.fastabend@...il.com>,
	<kvm@...r.kernel.org>, <virtualization@...ts.linux.dev>,
	<bpf@...r.kernel.org>
Subject: Re: [PATCH net-next 4/6] vhost/net: remove
 vhost_net_page_frag_refill()

On 2024/1/6 0:06, Alexander H Duyck wrote:
>>  
>>  static void handle_tx_copy(struct vhost_net *net, struct socket *sock)
>> @@ -1353,8 +1318,7 @@ static int vhost_net_open(struct inode *inode, struct file *f)
>>  			vqs[VHOST_NET_VQ_RX]);
>>  
>>  	f->private_data = n;
>> -	n->page_frag.page = NULL;
>> -	n->refcnt_bias = 0;
>> +	n->pf_cache.va = NULL;
>>  
>>  	return 0;
>>  }
>> @@ -1422,8 +1386,9 @@ static int vhost_net_release(struct inode *inode, struct file *f)
>>  	kfree(n->vqs[VHOST_NET_VQ_RX].rxq.queue);
>>  	kfree(n->vqs[VHOST_NET_VQ_TX].xdp);
>>  	kfree(n->dev.vqs);
>> -	if (n->page_frag.page)
>> -		__page_frag_cache_drain(n->page_frag.page, n->refcnt_bias);
>> +	if (n->pf_cache.va)
>> +		__page_frag_cache_drain(virt_to_head_page(n->pf_cache.va),
>> +					n->pf_cache.pagecnt_bias);
>>  	kvfree(n);
>>  	return 0;
>>  }
> 
> I would recommend reordering this patch with patch 5. Then you could
> remove the block that is setting "n->pf_cache.va = NULL" above and just
> make use of page_frag_cache_drain in the lower block which would also
> return the va to NULL.

I am not sure if we can as there is no zeroing for 'struct vhost_net' in
vhost_net_open().

If we don't have "n->pf_cache.va = NULL", don't we use the uninitialized data
when calling page_frag_alloc_align() for the first time?

> .
>