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

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Message-ID: <20260205164341.pJvni8kA@linutronix.de>
Date: Thu, 5 Feb 2026 17:43:41 +0100
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: Vadim Fedorenko <vadim.fedorenko@...ux.dev>
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>,
	Eric Dumazet <edumazet@...gle.com>,
	"intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>,
	"Keller, Jacob E" <jacob.e.keller@...el.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [Intel-wired-lan] [PATCH iwl-next v3] igb: Retrieve Tx timestamp
 directly from interrupt for i210

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).

Sebastian