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

[Vadim Fedorenko <vadim.fedorenko@linux.dev>]

On 05/02/2026 10:37, Loktionov, Aleksandr wrote:
> 
> 
>> -----Original Message-----
>> From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
>> Sent: Thursday, February 5, 2026 11:04 AM
>> To: Loktionov, Aleksandr <aleksandr.loktionov@intel.com>
>> Cc: Kurt Kanzenbach <kurt@linutronix.de>; Nguyen, Anthony L
>> <anthony.l.nguyen@intel.com>; Kitszel, Przemyslaw
>> <przemyslaw.kitszel@intel.com>; Paul Menzel <pmenzel@molgen.mpg.de>;
>> Vadim Fedorenko <vadim.fedorenko@linux.dev>; Gomes, Vinicius
>> <vinicius.gomes@intel.com>; netdev@vger.kernel.org; Richard Cochran
>> <richardcochran@gmail.com>; linux-kernel@vger.kernel.org; Andrew Lunn
>> <andrew+netdev@lunn.ch>; Eric Dumazet <edumazet@google.com>; intel-
>> wired-lan@lists.osuosl.org; Keller, Jacob E
>> <jacob.e.keller@intel.com>; Jakub Kicinski <kuba@kernel.org>; Paolo
>> Abeni <pabeni@redhat.com>; David S. Miller <davem@davemloft.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).