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

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Message-ID: <willemdebruijn.kernel.bbdefedfb87e@gmail.com>
Date: Sun, 08 Feb 2026 11:25:40 -0500
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Vadim Fedorenko <vadim.fedorenko@...ux.dev>, 
 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

Vadim Fedorenko wrote:
> 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.

Are you referring to sysctl_tstamp_allow_data?

That is enabled by default.

> To receive these timestamps users have to get
> CAP_NET_RAW permission, and it will work with the updated logic as well...