netdev - Re: [Intel-wired-lan] [PATCH iwl-next v3] igb: Retrieve Tx timestamp directly from interrupt for i210

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Message-ID: <601f0c4b-52d8-4b60-96bf-f2d65f8073d8@linux.dev>
Date: Fri, 6 Feb 2026 10:12:04 +0000
From: Vadim Fedorenko <vadim.fedorenko@...ux.dev>
To: Willem de Bruijn <willemdebruijn.kernel@...il.com>,
 Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
 Willem de Bruijn <willemb@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>, Eric Dumazet <edumazet@...gle.com>,
 "David S. Miller" <davem@...emloft.net>
Cc: "Loktionov, Aleksandr" <aleksandr.loktionov@...el.com>,
 Kurt Kanzenbach <kurt@...utronix.de>,
 "Nguyen, Anthony L" <anthony.l.nguyen@...el.com>,
 "Kitszel, Przemyslaw" <przemyslaw.kitszel@...el.com>,
 Paul Menzel <pmenzel@...gen.mpg.de>,
 "Gomes, Vinicius" <vinicius.gomes@...el.com>,
 "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
 Richard Cochran <richardcochran@...il.com>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 Andrew Lunn <andrew+netdev@...n.ch>,
 "intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>,
 "Keller, Jacob E" <jacob.e.keller@...el.com>
Subject: Re: [Intel-wired-lan] [PATCH iwl-next v3] igb: Retrieve Tx timestamp
 directly from interrupt for i210

On 05.02.2026 21:41, Willem de Bruijn wrote:
> Vadim Fedorenko wrote:
>> On 05/02/2026 16:43, Sebastian Andrzej Siewior wrote:
>>> On 2026-02-05 16:27:03 [+0000], Vadim Fedorenko wrote:
>>>>> So the only thing that bothers me is the read_lock_bh() in
>>>>> skb_may_tx_timestamp() which deadlocks if the socket is write-locked on
>>>>> the same CPU.
>>>>
>>>> Alright. Now you make me think whether we should enforce OPT_TSONLY
>>>> option on socket which doesn't have CAP_NET_RAW? Then we can get rid of this
>>>> check, and in case sysctl was flipped off - drop TX timestamps as
>>>> it's done now?
>>>
>>> This would "fix" this problem for all users which do deliver the
>>> timestamp from their IRQ handler instead of napi. There are a few of
>>> those…
>>> This would be considered stable material, right? (despite the fact that
>>> we have it for quite some time and nobody complained so far).
>>
>> cc: Willem as he is the author of the check introduced back in 2015.
>>
>> But it's more like a question to maintainers whether it is acceptable
>> way of "fixing" drivers or it's no-go solution
> 
> Requiring OPT_TSONLY unless CAP_NET_RAW would break legacy users.

Well, they are kinda broken already. Without OPT_TSONLY and CAP_NET_RAW all TX
timestamps are silently dropped. To receive these timestamps users have to get
CAP_NET_RAW permission, and it will work with the updated logic as well...