Re: [Internet]Re: [PATCH net-next v4 4/4] net: tun: track dropped skb via kfree_skb_reason()

From: Dongli Zhang <dongli.zhang@oracle.com>
To: "imagedong(董梦龙)" <imagedong@tencent.com>,
	"David Ahern" <dsahern@gmail.com>,
	"Jakub Kicinski" <kuba@kernel.org>
Cc: "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	"bpf@vger.kernel.org" <bpf@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"davem@davemloft.net" <davem@davemloft.net>,
	"rostedt@goodmis.org" <rostedt@goodmis.org>,
	"mingo@redhat.com" <mingo@redhat.com>,
	"ast@kernel.org" <ast@kernel.org>,
	"daniel@iogearbox.net" <daniel@iogearbox.net>,
	"andrii@kernel.org" <andrii@kernel.org>,
	"joao.m.martins@oracle.com" <joao.m.martins@oracle.com>,
	"joe.jin@oracle.com" <joe.jin@oracle.com>,
	"edumazet@google.com" <edumazet@google.com>
Subject: Re: [Internet]Re: [PATCH net-next v4 4/4] net: tun: track dropped skb via kfree_skb_reason()
Date: Wed, 2 Mar 2022 10:26:05 -0800	[thread overview]
Message-ID: <9ce6ca48-9199-dc9c-296a-7ad61fd1ac31@oracle.com> (raw)
In-Reply-To: <7991329A-DC69-4A6D-925D-33866EF5FB7E@tencent.com>

Hi Menglong,

On 3/1/22 8:16 PM, imagedong(董梦龙) wrote:
> 
> 
> On 2022/3/2 AM 11:29，“David Ahern”<dsahern@gmail.com> write:
> 
>> On 3/1/22 7:50 PM, Jakub Kicinski wrote:
>>> On Sat, 26 Feb 2022 00:49:29 -0800 Dongli Zhang wrote:
>>>> +	SKB_DROP_REASON_SKB_PULL,	/* failed to pull sk_buff data */
>>>> +	SKB_DROP_REASON_SKB_TRIM,	/* failed to trim sk_buff data */
>>>
> [...]
>>>>  	SKB_DROP_REASON_DEV_HDR,	/* there is something wrong with
>>>>  					 * device driver specific header
>>>>  					 */
>>>> +	SKB_DROP_REASON_DEV_READY,	/* device is not ready */
>>>
>>> What is ready? link is not up? peer not connected? can we expand?
>>
>> As I recall in this case it is the tfile for a tun device disappeared -
>> ie., a race condition.
> 
> This seems is that tun is not attached to a file (the tun device file
> is not opened?) Maybe TAP_UNATTACHED is more suitable :)
> 
> 

Thank you very much for the suggestions! TAP_UNATTACHED is more suitable.

The tap/tun are only two of drivers in linux kernel. We have already introduced
another two tap/tun specific reasons.

My concern is we may finally have too many reasons. That's why I am always
trying to define the reason as generic as possible so that they will be re-used
by most networking drivers.

We may expand the reason if it is fine to have too many reasons for skb_drop_reason.

Dongli Zhang