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: <6a0f4cbb-e8b3-4f0e-b7f1-7f9ca5cba97d@linux.dev>
Date: Thu, 5 Feb 2026 11:56:44 +0000
From: Vadim Fedorenko <vadim.fedorenko@...ux.dev>
To: "Loktionov, Aleksandr" <aleksandr.loktionov@...el.com>,
 Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc: 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 05/02/2026 10:37, Loktionov, Aleksandr wrote:
> 
> 
>> -----Original Message-----
>> From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
>> Sent: Thursday, February 5, 2026 11:04 AM
>> To: Loktionov, Aleksandr <aleksandr.loktionov@...el.com>
>> Cc: 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>;
>> Vadim Fedorenko <vadim.fedorenko@...ux.dev>; Gomes, Vinicius
>> <vinicius.gomes@...el.com>; netdev@...r.kernel.org; Richard Cochran
>> <richardcochran@...il.com>; linux-kernel@...r.kernel.org; Andrew Lunn
>> <andrew+netdev@...n.ch>; Eric Dumazet <edumazet@...gle.com>; 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: RE: [Intel-wired-lan] [PATCH iwl-next v3] igb: Retrieve
>> Tx timestamp directly from interrupt for i210
>>
>> On 2026-02-05 09:47:14 [+0000], Loktionov, Aleksandr wrote:
>> …
>>>> --- a/drivers/net/ethernet/intel/igb/igb_ptp.c
>>>> +++ b/drivers/net/ethernet/intel/igb/igb_ptp.c
>>>> @@ -796,6 +796,28 @@ static int igb_ptp_verify_pin(struct
>> …
>>>> +	igb_ptp_tx_hwtstamp(adapter); <-Calls existing function
>> designed for work queue!
>>>
>>> skb_tstamp_tx() can sleep
>>> Smells like sleep-in-atomic isn't it?
>>
>> How or where can it sleep?
>>
>> Sebastian
> 
> igb_ptp_tx_hwtstamp() -> https://elixir.bootlin.com/linux/v6.19-rc5/C/ident/skb_tstamp_tx -> https://elixir.bootlin.com/linux/v6.19-rc5/C/ident/__skb_complete_tx_timestamp -> https://elixir.bootlin.com/linux/v6.19-rc5/C/ident/sock_queue_err_skb -> https://elixir.bootlin.com/linux/v6.19-rc5/C/ident/skb_queue_tail -> https://elixir.bootlin.com/linux/v6.19-rc5/source/net/core/skbuff.c#L4075
> 
> spin_lock_irqsave(&wq_head->lock, flags);  <- RT mutex can sleep

Hmm... that actually means we have some drivers broken for RT kernels if
they are processing TX timestamps within a single irq vector:
- hisilicon/hns3
- intel/i40e (and ice probably)
- marvell/mvpp2

For igb/igc/i40e it's still OK to process TX timestamps directly in
MSI-X configuration, as ring processing has separate vector, right?

But in general skb_tstamp_tx should be moved to BH processing (NAPI poll
callback).