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

From: Willem de Bruijn <[email-masked]>
Date: Thu, 05 Feb 2026 16:41:03 -0500

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.